Yes its very true , and i think cuz my english is bad .
" I want to know how to setup a temporarily game with me and my friend over the internet. This server is not going to be permanently. "
I suggest you just port forward ports 27015, 27005 and then in garrysmod press “create multiplayer” after choosing map (and changing settings).
If your friend don’t see your server in his Friends tab, go here http://www.checkip.org/ and tell him to type (without quotes): “connect your_ip_here” in his console.
Click this - This will let you create a server for 4 hours.