I would suspect that the Files and Folders are in the wrong Locations.
Did the Car and Track Mods came as exe or as zip Files?
I would suggest to extract (if zip) or install (if exe) the Files into an empty folder, that you can create on e.g. the Desktop.
If you did that, open the folder and see what subfolderstructure it has.
If you see a folder called "GameData" with subfolders "Vehicles" and "Locations", copy all the extracted Folders and Files and paste them into your Steam Folder.
You have to look for the Folder "Steam\steamapps\common\rFactor 1".
Maybe the Folder "rFactor 1" is named different, i don't know how it is called in Steam, because i don't use the Steam Version.
If you open this Folder, you should also see the "GameData" Folder.
If you now paste the Mods Folders and Files here and get the Message that some Folders already exists and if you want to override them, click "yes" or "OK".
That should install things correctly and make them available in the Game.