wp add_action

function email_friends($post_ID) {
$friends = 'bob@example.org, susie@example.org';
mail($friends, "sally's blog updated" , 'I just put something on my blog: http://blog.example.com');
return $post_ID;
}

add_action('publish_post', 'email_friends');

function echo_comment_id($comment_ID) {
echo "I just received $comment_ID";
}
add_action('comment_id_not_found','echo_comment_id', 10, 1);

http://codex.wordpress.org/Function_Reference/add_action