Here is my guide which has been edited for public use!
First of, make a folder in 'My Documents' called 'rFactor Downloads', this is where you will be saving all rFactor downloads.
EXE's: The easiest! When you download the installer to your new folder (it may be RAR'ed up, so if it is right click it and select 'Extract Here') click the icon and 'send' it to were it tells you to... this is usually the rFactor root folder for cars and your 'Locations' folder for tracks.
Cars: Quite easy! When you download the file to your new folder, you should have a WinRAR file. Right click this and select 'Extract Here'. You now have the files in your 'rFactor Downloads' folder called 'GameData' and 'rFm'. You may have a few more like 'Movie Files' and 'UIData'... you do the same thing anyway.
Open up your rFactor root directory... in a different window of course (C:/Program Files/rFactor in theory), and just cut and paste the 'GameData', and 'rFm' files straight in (and any others that have come with it), when it asks you to overwrite, click 'Yes to All', and there you go, go racing with your new mod! When a new car update comes out, it will be in the same folder structure as 'GameData' blah blah blah... and you just do as normal, making sure you press 'Yes to All' when it tells you to overwrite!
Tracks: Hardest! When you download the file to your new folder, you should have a WinRAR file. Right click this and select 'Extract Here' (Lets pretend we are doing Norisring). You should now have the file in your 'rFactor Downloads' folder called Norisring or similar. Open up that folder and if it has a main folder in and a couple of small files, you just need to go back and cut and paste your first Norisring folder into your 'Locations' folder (C:/Program Files/rFactor/GameData/Locations in theory). Then you are done!
BUT if it has a poor file structure (you have to go through loads of folders to get to the main folder and small files together) you just go back one from the main folder and small files (just like we did before really), and there you go! Go race your new car on your new track!