General concepts

Firstly, if something is wrong or incomplete, and you know it, please fix it. You can do that by hitting the [edit] button anywhere. Don't panic, it is possible for the changes to be "rolled back". When you're done hit "Show preview" or "Save page"; it's as simple as that.

Documentation

Some real documentation can be found here: MediaWiki and for editing in particular: Editing

And if like me you didn't notice the little link on the left, here it is again: Help