Take a look in your rFactor install folder. You'll find a GameData folder.
Look in there, and you'll find a Locations folder - that's where tracks go. Just need to make sure you don't accidentally throw extra GameData\Locations folders into your GameData\Locations folder, since that won't work. (need to check what folders each track has... some have the full path, others you can just put straight into the Locations folder).
Also in there is a Vehicles folder, but mods usually have sounds and other things (that go into other folders within GameData) plus need some .rfm files which will go into the rFm folder, so when you open up a mod you'll normally see a GameData folder and an rFm folder. Just drag them into your rFactor folder and all the subfolders will be in the right place. But, again, you need to check what folders are in the archive and drag the correct ones out, or extract to a temp folder and work it out from there.
It's not a simple process until you're familiar with it, which is why I said to 'spend a good few minutes'. By that I mean 10, 15, 20
All this is assuming you have a version of rFactor that will let you play third-party mods (not the content-limited trial version), and you don't have Win Vista/7 UAC enabled and interfering with where things are stored (may not affect mods and tracks, I honestly don't know).
Probably 95% of error messages that come up after installing mods or tracks are due to putting folders in the wrong place, so it's worth getting comfortable with it. (at least until rF2, which sounds like it will avoid all this hassle)
For an overview of all the 'normal' defined folders, check out the config.ini in your rFactor folder.