Here is a
tutorial on how to create a standard vB page. Basically from there, look at other mods, vbulletin files or posts here to figure out other functions you can use. Other than that, it's just PHP.
$bbuserinfo ($vbulletin->userinfo in 3.5) contains all the users information, such as posts, username, userid, etc. $vboptions ($vbulletin->options in 3.5) contains all the options.. there are many more