How to play with my friend?

[no0nec4res]

Wnen I start server my friend can't connect to me. How can we play together coop?

[unconditional surrender]

"Hosting a multiplayer is as easy as setting up your own quickmatch game or campaign as shown previously, hitting “ESC” to get to the main menu, and then hitting the “Activate server” button.
1. Port number. **Please ensure this port is properly forwarded!
2. Your username. This will show up on the browser as the server name.
3. If you wish to make a public game, select yes. For private matches, select no.
4. Start the match.
5.Back to main menu.
Once you hit “Start!” the server will be open for connections. If people are having issues connecting with your server, please check to make sure that the port is properly forwarded. We will not go into details about how to do this. To get instructions on port forwarding, please do a Google search or check the manual of your router."

-Yes, this is shamelessly ripped straight out of the RWR handbook.
And i have absolutely zero knowledge about port forwarding or computers in general.
Good luck!