Do I use this mod? Want to spotlight it in my mod monday series but I cant figure out how to use it.

First I tried to put the rar into the mods folder like every other mod works but there are no cars

Then I read the Read.me and it says to put the files into a "plugin" folder, but where the heck is that folder? I searched everything in appdata and everything in the steam folder but there is no such folder thats called "appdata" ... than I put all 3 sub-folders from the mod into the main mod folder but again no new cars... wtf? xD