What is confusing about clicking Play > Multiplayer? Once you're there the server list will be fetched and you can join a game provided it's not passworded, full, or using mods you don't have. If you don't see any servers, try clicking in the top right to change from LAN to internet. Though internet should be default. I must say though, joining random multiplayer servers doesn't lead to the best experiences. Unless you're into Wasteland. But even then, it's better to be in a voip client with some friends to play with. You're welcome to play with us, though we have no predictable schedule.