Hi chmichel, welcome to ABB.
That's quite simple too ... exactly like the install ... without install of course
Just log in to the ABB-Homepage.
When you are logged in, the section "Teamspeak 3" (left side of HP) contains links. Simply select the link to the chatroom, you want to join (in this case "Setup-Guide" ).
That Link will open your TS3-client (if installed, otherwise, you'll get the client that way too) automatically connecting you to the selected chatroom/conversation.
Thats it.
Greets
Olaf