Register Sidebar dont work

You can register a new sidebar as a snippet like this:

add_action( 'widgets_init', function () {

	register_sidebar( array(
		'id'            => 'unique-sidebar-id', // make sure this is lowercase and unique
		'description'   => 'Sidebar description.',
		'before_widget' => '<li id="%1$s" class="widget %2$s">',
		'after_widget'  => '</li>',
		'before_title'  => '<h2 class="widgettitle">',
		'after_title'   => '</h2>'
	) );

} );

Of course, you will still need to output it somewhere in your theme. If you want to display it in a post/page content, you can add it as a shortcode:

add_shortcode( 'my_sidebar', function () {
	ob_start();

	dynamic_sidebar( 'unique-sidebar-id' );

	return ob_get_clean();
} );