In the recruitment stories sub-forum, there's a thread at the very top of the page that explains it in great detail.
ETA:
http://www.greekchat.com/gcforums/sh...ad.php?t=22514
Honestly, that thread will tell you everything you need to know. When you get toward the end, they even walk through example (fictional) campuses.
If you read it, and then you have specific questions, I think some expert GCers will be happy to answer them.