diff --git a/inc/class-wooviet-admin-page.php b/inc/class-wooviet-admin-page.php
index 6c9d500..9fe3477 100644
--- a/inc/class-wooviet-admin-page.php
+++ b/inc/class-wooviet-admin-page.php
@@ -13,17 +13,49 @@ if ( ! defined( 'ABSPATH' ) ) {
  */
 class WooViet_Admin_Page {
 
+	/**
+	 * @var string The message to display after saving settings
+	 */
 	var $message = '';
 
+	/**
+	 * WooViet_Admin_Page constructor.
+	 */
 	public function __construct() {
-
-		if (isset($_REQUEST['wooviet_nonce']) && isset ($_REQUEST['action']) && 'wooviet_save_settings' == $_REQUEST['action'])
+		// Catch and run the save_settings() action
+		if ( isset( $_REQUEST['wooviet_nonce'] ) && isset ( $_REQUEST['action'] ) && 'wooviet_save_settings' == $_REQUEST['action'] ) {
 			$this->save_settings();
+		}
 
-		add_action('admin_menu', array($this, 'register_submenu_page'));
+		add_action( 'admin_menu', array( $this, 'register_submenu_page' ) );
 
 	}
 
+	/**
+	 * Save settings for the plugin
+	 */
+	public function save_settings() {
+		if ( wp_verify_nonce( $_REQUEST['wooviet_nonce'], 'wooviet_save_settings' ) ) {
+			update_option( 'woocommerce-for-vietnam', $_REQUEST['settings'] );
+
+			$this->message =
+				'<div class="updated notice"><p><strong>' .
+				__( 'Settings saved', 'woocommerce-for-vietnam' ) .
+				'</p></strong></div>';
+
+		} else {
+
+			$this->message =
+				'<div class="error notice"><p><strong>' .
+				__( 'Can not save settings! Please refresh this page.', 'woocommerce-for-vietnam' ) .
+				'</p></strong></div>';
+		}
+	}
+
+	/**
+	 * Register the sub-menu under "WooCommerce"
+	 * Link: http://my-site.com/wp-admin/admin.php?page=woocommerce-for-vietnam
+	 */
 	public function register_submenu_page() {
 		add_submenu_page(
 			'woocommerce',
@@ -35,25 +67,9 @@ class WooViet_Admin_Page {
 		);
 	}
 
-	public function save_settings(){
-		if ( wp_verify_nonce( $_REQUEST['wooviet_nonce'], 'wooviet_save_settings') ){
-			update_option('woocommerce-for-vietnam', $_REQUEST['settings']);
-
-			$this->message =
-				'<div class="updated notice"><p><strong>' .
-				__('Settings saved', 'woocommerce-for-vietnam') .
-		        '</p></strong></div>'
-			;
-
-		} else {
-
-			$this->message =
-				'<div class="error notice"><p><strong>' .
-				__('Please refresh this page. Can not save settings!', 'woocommerce-for-vietnam') .
-				'</p></strong></div>'
-			;
-		}
-	}
+	/**
+	 * Generate the HTML code of the settings page
+	 */
 	public function admin_page_html() {
 		// check user capabilities
 		if ( ! current_user_can( 'manage_options' ) ) {
@@ -61,102 +77,138 @@ class WooViet_Admin_Page {
 		}
 
 		$settings = WooViet::get_settings();
-		//var_dump($settings); exit;
-
 
 		?>
-		<div class="wrap">
-			<h1><?= esc_html( get_admin_page_title() ); ?></h1>
-			<form name="woocommerce_for_vietnam" method="post">
+        <div class="wrap">
+            <h1><?= esc_html( get_admin_page_title() ); ?></h1>
+            <form name="woocommerce_for_vietnam" method="post">
 				<?php echo $this->message ?>
-				<input type="hidden" id="action" name="action" value="wooviet_save_settings">
-				<input type="hidden" id="wooviet_nonce" name="wooviet_nonce" value="<?php echo wp_create_nonce( 'wooviet_save_settings' ) ?>">
-				<table class="form-table">
-					<tbody>
-					<tr>
-						<th scope="row"><?php _e('Add provinces for Vietnam', 'woocommerce-for-vietnam')?></th>
-						<td>
-							<input name="settings[add_province][enabled]" type="hidden" value="no">
-							<input name="settings[add_province][enabled]" type="checkbox" id="add_province" value="yes"
-								<?php if('yes' == $settings['add_province']['enabled'] ) echo 'checked="checked"'?>>
-							<label for="add_province"><?php _e('Enabled', 'woocommerce-for-vietnam')?></label>
-						</td>
-					</tr>
+                <input type="hidden" id="action" name="action" value="wooviet_save_settings">
+                <input type="hidden" id="wooviet_nonce" name="wooviet_nonce"
+                       value="<?php echo wp_create_nonce( 'wooviet_save_settings' ) ?>">
+                <table class="form-table">
+                    <tbody>
+                    <tr>
+                        <th scope="row"><?php _e( 'Add provinces for Vietnam', 'woocommerce-for-vietnam' ) ?></th>
+                        <td>
+                            <input name="settings[add_province][enabled]" type="hidden" value="no">
+                            <input name="settings[add_province][enabled]" type="checkbox" id="add_province" value="yes"
+								<?php if ( 'yes' == $settings['add_province']['enabled'] )
+									echo 'checked="checked"' ?>>
+                            <label for="add_province"><?php _e( 'Enabled', 'woocommerce-for-vietnam' ) ?></label>
+                        </td>
+                    </tr>
 
-					<tr>
-						<th scope="row"><?php _e('Change VND currency symbol', 'woocommerce-for-vietnam')?></th>
-						<td>
-							<input name="settings[change_currency_symbol][enabled]" type="hidden" value="no">
-							<input name="settings[change_currency_symbol][enabled]" type="checkbox" id="change_currency_symbol" value="yes"
-								<?php if('yes' == $settings['change_currency_symbol']['enabled'] )echo 'checked="checked"'?>>
-							<label for="change_currency_symbol"><?php _e('Enabled', 'woocommerce-for-vietnam')?></label>
-							<br />
-							<br />
-							<input type="text" name="settings[change_currency_symbol][text]"
-							       value="<?php echo $settings['change_currency_symbol']['text']?>"
-							       id="change_currency_symbol_text"class="small-text">
-							<label for="change_currency_symbol_text"><?php _e('Insert a text to change the default symbol <code>đ</code>', 'woocommerce-for-vietnam')?></label>
-						</td>
-					</tr>
-					<tr>
-						<th scope="row"><?php _e('Convert <code>000</code> of prices to K (or anything)', 'woocommerce-for-vietnam')?></th>
-						<td>
-							<input name="settings[convert_price][enabled]" type="hidden" value="no">
-							<input name="settings[convert_price][enabled]" type="checkbox" id="convert_price" value="yes"
-								<?php if('yes' == $settings['convert_price']['enabled'] ) echo 'checked="checked"'?>>
-							<label for="convert_price"><?php _e('Enabled', 'woocommerce-for-vietnam')?></label>
+                    <tr>
+                        <th scope="row"><?php _e( 'Change VND currency symbol', 'woocommerce-for-vietnam' ) ?></th>
+                        <td>
+                            <input name="settings[change_currency_symbol][enabled]" type="hidden" value="no">
+                            <input name="settings[change_currency_symbol][enabled]" type="checkbox"
+                                   id="change_currency_symbol" value="yes"
+								<?php if ( 'yes' == $settings['change_currency_symbol']['enabled'] )
+									echo 'checked="checked"' ?>>
+                            <label for="change_currency_symbol"><?php _e( 'Enabled', 'woocommerce-for-vietnam' ) ?></label>
+                            <br/>
+                            <br/>
+                            <input type="text" name="settings[change_currency_symbol][text]"
+                                   value="<?php echo $settings['change_currency_symbol']['text'] ?>"
+                                   id="change_currency_symbol_text" class="small-text">
+                            <label for="change_currency_symbol_text"><?php _e( 'Insert a text to change the default symbol <code>đ</code>', 'woocommerce-for-vietnam' ) ?></label>
+                        </td>
+                    </tr>
+                    <tr>
+                        <th scope="row"><?php _e( 'Convert <code>000</code> of prices to K (or anything)', 'woocommerce-for-vietnam' ) ?></th>
+                        <td>
+                            <input name="settings[convert_price][enabled]" type="hidden" value="no">
+                            <input name="settings[convert_price][enabled]" type="checkbox" id="convert_price"
+                                   value="yes"
+								<?php if ( 'yes' == $settings['convert_price']['enabled'] )
+									echo 'checked="checked"' ?>>
+                            <label for="convert_price"><?php _e( 'Enabled', 'woocommerce-for-vietnam' ) ?></label>
 
-							<fieldset><br />
-								<input type="text" name="settings[convert_price][text]"
-								       value="<?php echo $settings['convert_price']['text']?>"
-								       id="convert_price_text" class="small-text">
-								<label for="convert_price_text"><?php _e('Choose what you want to change. E.g:', 'woocommerce-for-vietnam')?> <code>K</code>, <code>nghìn</code>, <code>ngàn</code></label>
-							</fieldset>
-						</td>
-					</tr>
-					<tr>
-						<th scope="row"><?php printf(__('Support VND for <a href="%s">the Paypal Standard gateway</a>','woocommerce-for-vietnam'), 'https://docs.woocommerce.com/document/paypal-standard/') ?></th>
-						<td>
-							<input name="settings[vnd_paypal_standard][enabled]" type="hidden" value="no">
-							<input name="settings[vnd_paypal_standard][enabled]" type="checkbox" id="vnd_paypal_standard" value="yes"
-								<?php if('yes' == $settings['vnd_paypal_standard']['enabled'] ) echo 'checked="checked"'?>>
-							<label for="vnd_paypal_standard"><?php _e('Enabled', 'woocommerce-for-vietnam')?></label>
+                            <fieldset><br/>
+                                <input type="text" name="settings[convert_price][text]"
+                                       value="<?php echo $settings['convert_price']['text'] ?>"
+                                       id="convert_price_text" class="small-text">
+                                <label for="convert_price_text"><?php _e( 'Choose what you want to change. E.g:', 'woocommerce-for-vietnam' ) ?>
+                                    <code>K</code>, <code>nghìn</code>, <code>ngàn</code></label>
+                            </fieldset>
+                        </td>
+                    </tr>
+                    <tr>
+                        <th scope="row"><?php printf( __( 'Support VND for <a href="%s">the Paypal Standard gateway</a>', 'woocommerce-for-vietnam' ), 'https://docs.woocommerce.com/document/paypal-standard/' ) ?></th>
+                        <td>
+                            <input name="settings[vnd_paypal_standard][enabled]" type="hidden" value="no">
+                            <input name="settings[vnd_paypal_standard][enabled]" type="checkbox"
+                                   id="vnd_paypal_standard" value="yes"
+								<?php if ( 'yes' == $settings['vnd_paypal_standard']['enabled'] )
+									echo 'checked="checked"' ?>>
+                            <label for="vnd_paypal_standard"><?php _e( 'Enabled', 'woocommerce-for-vietnam' ) ?></label>
 
-							<fieldset><br />
-								<select name="settings[vnd_paypal_standard][currency]" id="vnd_paypal_standard_currency">
+                            <fieldset><br/>
+                                <select name="settings[vnd_paypal_standard][currency]"
+                                        id="vnd_paypal_standard_currency">
 									<?php
-									$paypal_supported_currencies = array( 'AUD', 'BRL', 'CAD', 'MXN', 'NZD', 'HKD', 'SGD', 'USD', 'EUR', 'JPY', 'TRY', 'NOK', 'CZK', 'DKK', 'HUF', 'ILS', 'MYR', 'PHP', 'PLN', 'SEK', 'CHF', 'TWD', 'THB', 'GBP', 'RMB', 'RUB' );
-									foreach ($paypal_supported_currencies as $currency ) {
+									$paypal_supported_currencies = array(
+										'AUD',
+										'BRL',
+										'CAD',
+										'MXN',
+										'NZD',
+										'HKD',
+										'SGD',
+										'USD',
+										'EUR',
+										'JPY',
+										'TRY',
+										'NOK',
+										'CZK',
+										'DKK',
+										'HUF',
+										'ILS',
+										'MYR',
+										'PHP',
+										'PLN',
+										'SEK',
+										'CHF',
+										'TWD',
+										'THB',
+										'GBP',
+										'RMB',
+										'RUB'
+									);
+									foreach ( $paypal_supported_currencies as $currency ) {
 
-										if ( strtoupper($currency) == $settings['vnd_paypal_standard']['currency']){
-											printf('<option selected="selected" value="%1$s">%1$s</option>', $currency);
+										if ( strtoupper( $currency ) == $settings['vnd_paypal_standard']['currency'] ) {
+											printf( '<option selected="selected" value="%1$s">%1$s</option>', $currency );
 										} else {
-											printf('<option value="%1$s">%1$s</option>', $currency);
+											printf( '<option value="%1$s">%1$s</option>', $currency );
 										}
 
 									}
 									?>
-								</select>
-								<label for="vnd_paypal_standard_currency"><?php _e('Select a Paypal supported currency (like USD, EUR, etc), which is used to convert VND prices', 'woocommerce-for-vietnam')?></label>
-								<br />
-								<br />
+                                </select>
+                                <label for="vnd_paypal_standard_currency"><?php _e( 'Select a Paypal supported currency (like USD, EUR, etc), which is used to convert VND prices', 'woocommerce-for-vietnam' ) ?></label>
+                                <br/>
+                                <br/>
 
-								<input name="settings[vnd_paypal_standard][rate]" type="number" step="1" min="100" id="vnd_paypal_standard_rate" style="width: 70px;"
-								       value="<?php echo $settings['vnd_paypal_standard']['rate']?>"
-								<label for="vnd_paypal_standard_rate"><?php _e('Insert the exchange rate of this currency to VND', 'woocommerce-for-vietnam')?></label>
-							</fieldset>
+                                <input name="settings[vnd_paypal_standard][rate]" type="number" step="1" min="100"
+                                       id="vnd_paypal_standard_rate" style="width: 70px;"
+                                       value="<?php echo $settings['vnd_paypal_standard']['rate'] ?>"
+                                <label for="vnd_paypal_standard_rate"><?php _e( 'Insert the exchange rate of this currency to VND', 'woocommerce-for-vietnam' ) ?></label>
+                            </fieldset>
 
-						</td>
-					</tr>
-					</tbody>
-				</table>
+                        </td>
+                    </tr>
+                    </tbody>
+                </table>
 
-				<p class="submit">
-					<input type="submit" name="submit" id="submit" class="button button-primary" value="Save Changes">
-				</p>
+                <p class="submit">
+                    <input type="submit" name="submit" id="submit" class="button button-primary" value="Save Changes">
+                </p>
 
-			</form>
-		</div><!-- #wrap ->
+            </form>
+        </div><!-- #wrap ->
         <?php
 	}
 
diff --git a/woocommerce-for-vietnam.php b/woocommerce-for-vietnam.php
index 0568818..a31f971 100644
--- a/woocommerce-for-vietnam.php
+++ b/woocommerce-for-vietnam.php
@@ -32,12 +32,9 @@ new WooViet();
  */
 class WooViet {
 
-	protected $Provinces;
-	protected $Currency;
-	protected $VND_Paypal_Standard;
-
-	// protected $settings;
-
+	/**
+	 * @var array The default settings for the whole plugin
+	 */
 	static $default_settings = array(
 		'add_province'           =>
 			array(
@@ -60,6 +57,17 @@ class WooViet {
 				'rate'     => '22770',
 			),
 	);
+	/**
+	 * The properties to manage all classes under the "inc/" folder
+	 * Example:
+	 * - File name: class-wooviet-provinces.php
+	 * - Class Name: \WooViet_Provinces
+	 * - Method Name: WooViet->Provinces
+	 */
+	protected $Provinces;
+	protected $Currency;
+	protected $VND_Paypal_Standard;
+	protected $Admin_Page;
 
 	/**
 	 * Setup class.
@@ -75,9 +83,9 @@ class WooViet {
 	public function init() {
 
 		if ( is_admin() ) {
-			// @todo: Add the admin setting page
+			// Add the admin setting page
 			include( WOO_VIET_DIR . 'inc/class-wooviet-admin-page.php' );
-			new WooViet_Admin_Page();
+			$this->Admin_Page = new WooViet_Admin_Page();
 
 		}
 
@@ -114,6 +122,14 @@ class WooViet {
 
 	}
 
+	/**
+	 * The wrapper method to get the settings of the plugin
+	 * @return array
+	 */
+	static function get_settings() {
+		return get_option( 'woocommerce-for-vietnam', self::$default_settings );
+	}
+
 	/**
 	 * Localize the plugin
 	 * @since 1.0
@@ -122,9 +138,4 @@ class WooViet {
 		load_plugin_textdomain( 'freshfunbits', false, basename( dirname( __FILE__ ) ) . '/languages/' );
 	}
 
-	static function get_settings() {
-
-		return get_option( 'woocommerce-for-vietnam', self::$default_settings );
-	}
-
 }
\ No newline at end of file