shortcode wordpress form

function user() {     
 ob_start();
 include(get_stylesheet_directory() . '/tutorial.php');
 return ob_get_clean();
}
add_shortcode( 'countdown', 'user' );

public function add_shortcode_fileds() {
    add_shortcode( 'add_fields', 'input_fields' );
    function input_fields( $atts ) {
        $atts='<form method="post" action="">';
        $atts.='<input type="text">';
        $atts.='<input type="submit">';
        $atts.='</form';
        return $atts;
    }
}