This was originally just a home for character sheets to be used with play-by-post games. However, it has been expanded into a general campaign site to keep track of campaign settings, definitions, rules, etc.
Each campaign has their own home page:
To create a new page, simply type your page name in the search box and search. When it doesn't find a result, there will be a button to "create this page." Right now we don't have any namespace rules, but it's best if you keep all of your pages within your campaign namespace (i.e. directory), just create it using the same method. A page named "home" is the default page for any namespace.
For example, if I wanted to create a new campaign called Phantasie and have everything for my campaign in its own namespace, first I would type "/Phantasie/home" in the search box and create that page. Later, if I wanted to create a page for the City of Glantri in my namespace, I would type "/Phantasie/City of Glantri" in the search box and create it.
Alternatively, you can simply create pages within a namespace (directory) simply by creating a link on another page in that namespace. For example, instead above I could simply create a link for "City of Glantri" on my campaign home page, save, click the link, and create the page.
The software here operates a little differently than what you typically find with MediaWiki (Wikipedia's software). here is a list of notable differences:
Want to have a paper copy of your character on a traditional character sheet? Use this one.