This wiki contains some basic information about MP2, but is still missing many content. So besides the wiki you also can look for information at MediaPortal 2's issue tracker (JIRA) or within the MediaPortal 2 forums (English, German).
If you would like to contribute to the documentation or in any other way take a look at the contribution guide.
Feel free to create new threads in the forums if you can not find the information after using the search in wiki, forum or issue tracker.
Last but not least: Have fun !!! :)