Please consult the MediaWiki FAQs for questions about editing and creating pages on this site.
Wikipedia has an introductory tutorial.
Making a new wiki page
To create a new wiki page, simply edit the URL of this page, by replacing the words 'Help:Contents' with 'your page name'. Spaces in the URL should be replaced with '_'. For example, http://math.berkeley.edu/~mgsa/w/index.php/Boring_Example. Then just edit that page as you see fit: you can simply enter the text of your page, or you can make a more elaborate page if you know a bit of wiki markup. Look at the edit pages of some of the other wiki pages to get an idea for the special commands for getting things like section headings or italics. Please only use the characters A-Z a-z 0-9 . _ \ / ~ % - + & : ? ! = ( ) @ unless you know the special wiki uses of other characters, such as ] or *. These special characters might cause unexpected results.
And it's always smart to preview your post to make sure it displays the way you want it to.