Need help explaining how to use a VPN on a UNIX server with a Mac OS

I have gotten a gig to teach someone how to use a VPN client for a UNIX server on a MAC os. The problem is I have never used UNIX, dont mess with VPN's (my dad has a VPN that I have used a couple of times). I'm currently taking a crash course on UNIX but I was wondering if anyone could help me with the finer points. Maybe any help on using a vpn on unix?