WikiText, sometimes called wiki markup or markdown, is the simple code typed into the edit box that formats your writing in a wiki. Here at AboutUs, we use the simplified form of WikiText used by the Mediawiki software, which is much easier than learning HTML. The most important bit is to use the double bracket syntax, like [[link]] - to make internal WikiLinks.

A good guide to basic WikiText can be found here, and some fancier templates to enhance your WikiText can be found at the AboutUs Template list.