function skrypt_dodawanie() {
    wp_enqueue_style( 'my-plugin-css', plugins_url('/assets/css/plugin.css', __FILE__) );
    wp_enqueue_script( 'my-plugin-js', plugins_url('/assets/js/jquery.js', __FILE__), array('jquery'));
}
add_action('wp_enqueue_scripts', 'skrypt_dodawanie');