Do you have to use a file extractor thing or is it like BeamNG where you download the mod and drag it to the folder?
Usually, the mod will be a .zip or a .rar file and you have to extract it to the right folder. If you're using Content Manager you can just drag it over Content Manager's window, click the three lines just next to the minimize window button and then click 'Install', CM will (usually) do the rest.