How to write proper manifest

Hi! I made something like an extension - it adds google maps api image to profile, but I'm not able to write proper manifest. I don't really understand this hooks :<.

The only thing my little extension do is changing $forum_page['user_info']['location'] value in profile.php to

            $forum_page['user_info']['location'] = '<li><img src="http://maps.googleapis.com/maps/api/staticmap?center='.$user['location'].'&size=250x200&sensor=false&maptype=terrain6&markers=size:small%7Ccolor:blue%7C'.$user['location'].'\"/></li><li><span>'.$lang_profile['From'].': <strong> '.forum_htmlencode(($forum_config['o_censoring'] == '1') ? censor_words($user['location']) : $user['location']).'</strong></span></li>';

Effect:

But how to write manifest to that?

It would be also cool to let user decide whether he want or not display map in his profile. I understand it would need new table in database, containing boolean variable, checkbox in Settings and some condition in profile display. But as i said, i don't understand hooks :<.