So far as I know, there are two ways.
1. If you're playing with friends on messenger (or similar) then go to
http://www.whatismyipaddress.com/) and give your friends your IP address. Then start JA and Create Game as normal. When your friends start JA, they bring the console down (Shift + `) and type \connect <ip address here>. You can copy and paste the IP into the console to save typing it out. They'll then be in the game with you hosting, but the game won't show up on the in-game server-list.
2. Start JA and go to Create Game. Check the box for Dedicated Server. When you start, you'll get the console window only. Then start JA again and the server you just created should be on the server-list and you and your friends can play as normal. However, as you're running 2 instances of JA, I think your ping may suffer for it, I know mine does :(
Hope that helps,
:) B