Example of WordPress Hooks and filters

lwp-announcement.php

<?php
/**
 * Plugin Name: LWP Announcement
 * Description: LWP Announcement
 * Version: 1.0.1
 * Author: Lax Mariappan
 */

add_action('wp_head', 'my_announcement');
 /**
  * Register the announcement action.
  */
 function my_announcement() {
   do_action('announcement_action');
 }
 
add_filter('announcement_filter','my_filter',10,2);
/**
 * Filters the announcement text.
 */
function my_filter($text, $name){
    return $text . ' filtered' . $name;
}

add_action('announcement_action','show_announcement');
function show_announcement(){
    $announcement = apply_filters('announcement_filter', '<p>This is my announcement</p>','Lax');
    echo $announcement;
}