You can login simply by writing in the console:
Code:
wsrv_login Name Password
where Name = your name and Password = your password
To create a game, you must simply log in.
To join a game, press ESC-->Multiplayer--> you should firstly your server and then his/her server here.
You can also join by writing in the console:
where IP = the guy's ip (the guy that made the server). To see your ip, you can go to this site:
http://www.whatismyip.com.
If you want somebody to join you, make sure you are logged in and the other person too! (else it might take you to a startmap with no teleporters)