That is hard to answer in general, because it depends on in which way the the modder putted the folders/files in the zip-file.
That can be for example:
-the complete folder structure like GameData/Locations/Trackfolder
in that case you'll have to unzip into your rFactor installation-folder
-only the Trackfolder
in that case you'll have to unzip into your GameData/Locations-folder
-a structure like: Trackname-folder/GameData/Locations/Trackfolder
in that case you'll have to unzip into a new folder and move the GameData with all content into your rFactor installation-folder
If you still have problems, please post a downloadlink of the track(s), then i can tell you what to do.