How to create Shortcode function in WordPress?

Users can make shortcodes with the use of WordPress Shortcode API, as it enables users to take benefits of existing theme features from any test-based area on WordPress site.

The shortcode functions can be created in three simpler steps-

1. Create function in function.php and register
function display_related_posts($array = array()) {
   <div class="col-md-12 remove-padding m-t20">Shortcode function defination</div>
}
add_shortcode('display_related_posts', 'display_related_posts');

2. Now you can call anywhere in file or editor with this function.
do_shortcode('[display_related_posts]');