Hopefully this wiki was put together well enough to make being an admin easy. However, there are a few things that might catch you off-guard.
In order to get rid of the sidebar, I modified MediaWiki:Common.css. Several of the rules are quite strange looking. If you don't know CSS, be careful. Firebug (Firefox extension) makes it a lot easier to write correct rules.
Special pages allow you to do many nifty things. Usually there is a sidebar link for them, but due to the stylesheet, this link no longer shows up. The list of all pages is Special:SpecialPages.
If your account has bureaucrat privileges, you can go to Special:ConfirmAccounts to approve people who have tried to create an account. This system was put in place to prevent tons of people from creating accounts.
It's probably a good idea to check every so often to make sure vandalism isn't happening. The list of recent changes is Special:RecentChanges.