PHP

wordpress create shortcode

function create_shortcode(){
    return "<h2>Hello world !</h2>";
}
add_shortcode('my_shortcode', 'create_shortcode');
// Use [my_shortcode]

wordpress do shortcode

<?php echo do_shortcode('[name_of_shortcode parameters=""]'); ?>

wordpress shortcode

function wp_demo_shortcode() { 

//Turn on output buffering
ob_start();
$code = 'Hello World';
ob_get_clean();

 // Output needs to be return
return $code;
} 

// register shortcode
add_shortcode('helloworld', 'wp_demo_shortcode'); 

wp shortcode

<?php echo do_shortcode("[name_of_your_shortcode]"); ?>

shortcode in wp

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