Hosting private server

#1
Hello, I bought recently this game with a friend but we can't play together because of this system. We are still wondering how to CREATE a server. There is no tutorial available.
I made the "port forwarding" thing but it don't work. Firewall isnt blocking Barotrauma.
So whats the issue ?? When my friend try to connect to my server, it fails because the game can't "translate my IP adress"...
Can someone help me ?
Sorry for my english btw i'm not a native english speaker