WordPress at a glance
function is not described

stick_post() WP 2.7.0

Make a post sticky.

Sticky posts should be displayed at the top of the front page.

Hooks in function
Return

Nothing (null).

Usage

stick_post( $post_id );
$post_id(int) (required)
Post ID.

Code of stick post: wp-includes/post.php VER 5.0.3

<?php
function stick_post( $post_id ) {
	$stickies = get_option('sticky_posts');

	if ( !is_array($stickies) )
		$stickies = array($post_id);

	if ( ! in_array($post_id, $stickies) )
		$stickies[] = $post_id;

	$updated = update_option( 'sticky_posts', $stickies );

	if ( $updated ) {
		/**
		 * Fires once a post has been added to the sticky list.
		 *
		 * @since 4.6.0
		 *
		 * @param int $post_id ID of the post that was stuck.
		 */
		do_action( 'post_stuck', $post_id );
	}
}