2den: You didn't download any extra cars, but only modified meshes that alter car's appearance and possibly it's performance. These mods just replace cars that already are in the game. As for the tracks, I'm not aware of any way how you can get any modified tracks to LFS. There are layouts, but these are only available in S1/S2.
Modified car meshes contain .vob files, so you use these to replace the original .vob files. According to the forum rules I'm not allowed to help you any further, sorry.