How do I use downloads or mods?

One of the most common questions asked by people that are new to the game or community.

How do I use downloads or mods?
Downloads, modifications or mods can be downloaded from many websites, they often come in three major formats;


 * .zip (Zip or compressed folder)


 * .rar (WinRAR archive)

Once you have downloaded or opened the archive, it should contain a *.ar file or an installer or setup, along with a few various other files, such as readme.txt and maybe an image of the vehicle.
 * .7z (7zip archive)

Related
Where is my game installed?