Seeing Servers

[Ataros]

He can probably direct connect to you if he can to other servers.

Alternatively ask him go to Steam -> Servers and add your IP to Favorites as a Favorit server. It will not appear in Steam but it will appear in game >> Multiplayer >> Client >> Favorites.

In case your provider puts you behind a router your server will not be visible in Client section but you can start server in Lobby section to make it visible from behind a router.