0) At the bottom of every page is a link "Edit Text of this Page". Click this link to, you guessed it, edit the text of the current page. To avoid wiki spam, you now have to login to PickWiki before doing this - see CanBeEdited.
1) Making a new page
2) If you post source code, surround it with PRE tags to keep the wiki from making a link out of every class and variable name. Watch out for trailing "\" characters at the end of lines. Even within a <PRE> section this appears to escape the end of line character and smush lines together.
E=\!sudo shutdown -h now PRINT "Are you sure you want to shutdown?"
VS.
E=\!sudo shutdown -h now \; PRINT "Are you sure you want to shutdown?"
3) Some formatting hints:
For more details see: [Text Formatting Rules]
4) Formatted source code tends to be a dead-end, so put a link like 'Back to JavaSource' at the top of the page.
5) Clicking on the link at the top of every page that matches the page title, will give a reverse index - a list of all pages that link to this one.
6) To include an external url, either just put it in the text, or you can create a link by putting the url in single square brackets. A description to go in the link can go after the url separated by a space -
[http://www.usemod.com/cgi-bin/wiki.pl?TextFormattingRules Text Formatting Rules]