How to Set Up a VPN Server with Mountain Lion OS X Server?

I have the Mountain Lion OS X 10.8.3 software and recently got the OS X Server app. I would like to set up a VPN server for me and my friend so we can play a game over LAN (or WAN, whatever you want to call it) but I'm not sure how to set it up. Can someone give me step by step instructions as to how to do that? Someone who has set this up before and it has worked for them... Thanks!