If you have me as a friend(same name as here) on steam, my account has been hacked so unless I post otherwise don't click any links that are sent from my account.
Go to multiplayer, go to player match, go to Custom, then continue to set the private slots allowed, usually do max if you want a bunch of your friends to join. Then start it and invite your friend. You can set the match settings how you want them as soon as you start the match.