管理面板中未显示菜单

I try to make my own theme in wordpress. Stucked a problem: i can't see menu button in admin panel. I've registered menu in functions.php of my theme

<?php
register_nav_menu( 'menu', 'Menu on the main page' );
    ?>

But there is no menu button appear in admin panel - appereance. I did all that was recommended on youtube video (https://youtu.be/I0zu6Dc3JDI?t=95). Nothing. Please help =) I have last version of Wordpress.

You was half way there, you had the right idea for registering the menu however you missed out telling WordPress to run your register menu command.

What you need to do is wrap it in a function and call the function on 'init' which is the initialisation of the admin area (one of many WordPress hooks), see below:

function register_child_menus() {
    register_nav_menus(
        array(
            'my-menu' => __( 'My Menu' )
        )
    );
} add_action( 'init', 'register_child_menus' );