Cant install cars or tracks

Hey peeps, new boy to the forums here and Ill apologise if Im making a n000b mistake here. Ive followed the guides on how to install the cars and tracks but nothing is coming up in my list of mods to allow me to install it. Ive added the file in the correct place and Ive also tried manually looking for the folder but nothing is coming up in the mod manager. Any advise? ...