I want to show an example of code that I myself recently found and I think it will be a good addition to the lesson “Create plugin and admin panel menu with add_menu_page“. Presented below code snippet add menu with submenu. You can use this code as for plugin development, so to develop your own WordPress themes.

To test a piece of code, go to your test site in the template folder, to file functions.php paste the code:

function theme_options_panel(){
  add_menu_page('Theme page title', 'Theme menu label', 'manage_options', 'theme-options', 'wps_theme_func');
  add_submenu_page( 'theme-options', 'Settings page title', 'Settings menu label', 'manage_options', 'theme-op-settings', 'wps_theme_func_settings');
  add_submenu_page( 'theme-options', 'FAQ page title', 'FAQ menu label', 'manage_options', 'theme-op-faq', 'wps_theme_func_faq');
}
add_action('admin_menu', 'theme_options_panel');
function wps_theme_func(){
                echo '<div class="wrap"><div id="icon-options-general" class="icon32"><br></div>
                <h2>Theme</h2></div>';
}
function wps_theme_func_settings(){
                echo '<div class="wrap"><div id="icon-options-general" class="icon32"><br></div>
                <h2>Settings</h2></div>';
}
function wps_theme_func_faq(){
                echo '<div class="wrap"><div id="icon-options-general" class="icon32"><br></div>
                <h2>FAQ</h2></div>';
}

After pasting the code, you will have menu Theme menu label and three sub menu Theme menu label, Settings menu label, FAQ menu label. I think further, if you read the section “For plugin development”, it will not be hard to figure out where to insert the code for each menu item.