How to host a server

See Here in the manual

How to host a server (in summary):
 * 1) Be sure you've forwarded port 1234 UDP (default port) on your router.
 * 2) Create or continue a Campaign / Quick match.
 * 3) Open „ESC“ menu, then click „Activate server“, configure and press „Start“ to activate the server.

NOTE ''Adding your host to the public servers will make it visible in the server list, if you want to play in private, choose „No“ and just share your IP and Port with your teammates. Players can join your server via Manual IP joining in the Menu.''