You will usually end up with either exe files or zip files. When the download finishes you need to extract all the files within the rar file.
Once the file has downloaded just double click on it and when it runs it will install itself, done, run the game and test it. When you download a mod file it will usually come in one of three file types.
How to install Farming Simulator 2019 / 19 Mods on PC
