how to display a specific wordpress menu?

Register your navigation menu

Add this code to your functions.php file.

function my_custom_new_menu() {
      register_nav_menu('my-custom-menu',__( 'My Custom Menu' ));
}
add_action( 'init', 'my_custom_new_menu' );

Create new menu

You can now go to Appearance » Menus page in your WordPress admin and try to create or edit a new menu. You will see ‘My Custom Menu’ as theme location option.

Display new menu

wp_nav_menu( array( 
    'theme_location' => 'my-custom-menu') 
);