How to save the setups:

1 - Download the setup you want to try;

2 - Go to your Documents folder and then follow this path: My Games/SimBin/User Data/Car Setups/TrackOfChoice/TrackLayout/ then you can paste the setup there;

3 - Load up the game with the car you want, go into the setups screen and load the setup as you normally would (top left folder icon in the setup screen and then select your setup).

If you dont see a track/layout folder in your Car Setups folder that means you haven't saved a setup beforehand and you must do so (You can just load up a practice session and go into the setup screen and save a setup with a basic name). Then the folders will be created, and you will be able to load up your downloaded setups.

Sometimes there are cars which are featured in different classes. If a setup is made for DTM for example, but you want to use it on GTR 3 you need to eather take the version made for it or just copy it over with the keycombinations ctrl + c and ctrl + v.