hi,
this is very easy to make.
go in your main GTL folder (pehaps root folder is name?? i am not good in english, so explain is not easy sometimes for me).
here you see something with name GTL DEDICATED,
click this on (perhaps with right click, and do start as admin, but not sure if this must be in your GTL version, but normaly not),
then comes a menü, where you can select the cars, the tracks, practise,quali and racelenghts and any other things too, important is, to select CONNECTIONE TO LOBBY (click on), which is under the trackfolder menü.
there are any things to select, but not realy difficulty, but perhaps you must try 2-3 times before you are happy with your settings.
and of course, you and your friend must both have installed the altbierbude lobby patch (and come in altbierbude too, which is for any people not easy sometimes).
that is all, very easy to make, hope you understand my english,
perhaps someone can better explain
servus
edit...and you and your friend must have both have idenical files (not editing in carfiles, or other things) and if you have installed addon cars/tracks, this your friend must have installed too, or your friend will not come in your server and get a "cheat warning".