Start a LAN game: This starts a LAN session on your machine. To do that, hit the red "open for lan" button in singleplayer menu. People who live in the same household can join to your local IP then. You can also play over the internet, but this requires port-forwarding. Usually it's recommendable to use the "play with friends" option instead, unless you want to play with users who don't have the Steam version of the game.
When I start the server, i make sure to check if everything's working. I generally use canyouseeme.org to check if my port is responding.
I portforwarded port 7777 which is the port I generally use to host my game servers. My friend tried to connect but he had a authentication problem.
I use the Standalone version of the game, and he uses the steam one, does that influence something?
about the 'Start a LAN game'.
Hm, this require forwarding. Which ports need to be forwarded for your LAN game to work? Do everyone has to have the Steam version of the game?
"Do not leave grudges and anger, let them miss you."