Couple of questions..

[FlyingStone]

Hello,
I am attempting to setup a dedicated server for GarrysMod version 10. However i seem to be getting mixed messages on somethings. I need to port forward Garry's Mod, i do use a router and i believe that is the problem. I do run Norton Anti virus, and Internet Security when ever i am on the computer and i rather not compromise those programs, or shut them down. My question is what do i port forward? Half life 2 Steam? or something entirely else? I plan on running this server not 24/7 but just for a couple of friends that i have, for a short while.
If anyone can help me i will be most grateful, if not is there another form or website that explains what to do in further detail?
Thank you very much,
-F.S