Help:Contents
If you ever visited and tried to edit Wikipedia then you should be very familiar with all this.
They have a guide there, and at the page of the creator of this wiki engine, you can read even more: Mediawiki user's guide to editing
Other languages:
- in czech language ;) - http://cs.wikipedia.org/wiki/Wikipedie:Jak_editovat_str%C3%A1nku
more advanced features: