This article, although old, covers the basics. What I find crap is that you need to copy the /usr/share/moin/data and underlay directories into wherever your wiki is going to live.
If you don't do this, moinmoin will helpfully give you an error saying the data directory doesn't exist or has the wrong permissions. In my case, the directory did exist with the right permissions: the problem was it didn't have all the other subdirectories needed that you get from the copy operation. Yay for clear error messages.