I haven't tried to host or join a game, but click on the "Match Maker" button near the top left side of this page (the middle one) and then follow your nose
. It appears to be fairly simple to create a new game (click the button?) and I'm assuming if you click on one of the open games, a join button will appear.
If you run into troubles with routers, ports, firewalls, etc., someone in the main room may be able to assist you. Failing that, post again and someone reading the forums should be able to assist you!
Armand