Hello there,
At first, take care that your firewall allows RFactor to connect to the internet
If the autoupdater finished, it will have given you a message like " ready, have fun" or solething like that. Then you have to start RFactor, go to the multiplayer menu and look for the bockbier-servers in the lobby. If you sort the server alphabeticaly in decreasing order, the server are listed in the higher level of the lobby list.
They look like
www1.bockbierbude... To
www7.bockbierbude
After you found them you just click the one you wanted and the in the right lower corner on the screen, in german its called" Beitreten" in english could be something like join.
Then you will get to the car selector. Take a car from ghe list, hit join again and after that you should be in the garage.