Help:Edits
This wiki is powered by MediaWiki, the same software that is used by Wikipedia. Therefore, the best thing you can do to learn how to edit wiki pages is to read some of the excellent MediaWiki editing guides:
90% of what you need to do is covered by the first link above. Even if you've never edited in a MediaWiki before, you can pick the basics up in less than half an hour.
When playing around, feel free to use the sandbox.
When you're ready to tackle an actual article, if you don't know what to write about, try taking a look at Special:Wantedpages.