where to create a shortcode in wordpress code example

Example 1: wordpress do shortcode

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

Example 2: wordpress create shortcode

// function that runs when shortcode is called
function wpb_demo_shortcode() { 
 
// Things that you want to do. 
$message = 'Hello world!'; 
 
// Output needs to be return
return $message;
} 
// register shortcode
add_shortcode('greeting', 'wpb_demo_shortcode');