An example of registering multiple menus in WordPress.

functions.php

function register_my_menus() {
  register_nav_menus(
    array(
      'new-menu' => __( 'New Menu' ),
      'another-menu' => __( 'Another Menu' ),
      'an-extra-menu' => __( 'An Extra Menu' )
    )
  );
}
add_action( 'init', 'register_my_menus' );