check out the official mediaWiki Help:Editing for a complete guide!
Quick guide to wiki editing
<nowiki>= Heading 1 = == Heading 2 == I am ''italic'' and I'm '''bold''' text. What about * some * fine ** lists? Or some even finer # numberd ## wiki # lists? Maybe a link to the [http://gp2x.72dpiarmy.com outside world] or one to the [[Main Page]] in the wiki? Why not use a custom [[Main Page|wiki link name]]? Did you know that you can use <div style="background-color: red">HTML</div>? Source code starts with a blank so do empty lines in code Alternative: <pre>
I am italic and I'm bold text.
Or some even finer
Source code starts with a blank so do empty lines in code
To structure the Wiki and make users aware of other interesting pages try to categorize your content. See Special:Categories for a list of existing categories.
To add a new category just add
to the bottom of the pages (multiple such Category tags if required). If the category page doesn't exist yet just edit it and add a brief description of the category. For more help see the mediawiki category help page.
Redirect / Redirecting a page
#REDIRECT [[Target Page]]
How to sign your name on discussion pages
You should sign your contributions by typing three or four tildes:
(~~~ = Username) (~~~~ = Username 19:36, 10 January 2006 (UTC)).
How to add images
The quick and dirty way: just write the link to the image, the wiki will embedd it automatically. For more info (also contains file uploads) view 
The "right" way: see the Images and other uploaded files MediaWiki User's Guide entry.