How to add custom menu to dashboard (or remove)

functions.php

<?php
/* 

Reference @codex:
- Add menu: https://codex.wordpress.org/Function_Reference/add_menu_page
- Select icon: https://developer.wordpress.org/resource/dashicons/#menu

- Remove menu: https://codex.wordpress.org/Function_Reference/remove_menu_page
- Remove sub-menu: https://codex.wordpress.org/remove_submenu_page

*/

add_action( 'admin_menu', 'register_custom_menu' );
function register_custom_menu() {
//add_menu_page( $page_title, $menu_title, $capability, $menu_slug, $function, $icon_url, $position );
	add_menu_page( 'Menús', 'Menús', 'manage_options', 'nav-menus.php', '', 'dashicons-menu', 21 );
}