when you;re on the wiki, click "create an account or login" in the upper right hand corner. Then create an account, then login. Once you'e logged in, you should see an additional tab "Edit" at the top of every page, where you can edit the page.
The content of the page is written pretty much like HTML.
To create a new page, load the page you want to create like this:http://wiki.linuxmce.org/index.php/My_New_Page_Name
And then again the edit tab will help you populate this page.
I hope this helps.