During the extended February 20–24 weekend, this website and the SIGSEM mailing list are migrated to a new server. There may be bumps ahead.
There isn't any help here, but you can go and look at these links
For a quick start, find out all about MediaWiki markup.
If you would like to use (La)TeX formulas in wiki pages, see Help:TeX.
For the adventurous, here is the Semantic MediaWiki manual.