The Time Lord Academy/How does one add a citation?

From Tardis Wiki, the free Doctor Who reference

I've done page edits before, but I've never added a citation. How does one go about that? I haven't tried on Wikipedia, and the only edits on other Wikia sites were either minor ones, or were extremely informal, and didn't require citations. On the wiki I got started on, everyone pretty much already knew everyone and the Admins would remove misinformation and block the users responsible as soon as it came up.