// functions.php
register_nav_menus([
    'primary' => __('Primary Menu', 'jesnin-theme')
]);

function mytheme_widgets_init() {
    register_sidebar([
        'name' => __('Sidebar', 'jesnin-theme'),
        'id' => 'sidebar-1',
        'before_widget' => '<!--div class="widget"-->',
        'after_widget' => '</div>',
        'before_title' => '<h2>',
        'after_title' => '</h2>'
    ]);
}
add_action('widgets_init', 'mytheme_widgets_init');