If the .rar contains a .scs file, move it directly here. If it only contains folders, the mod might be outdated or specifically for a different game.
You will typically find folders named data and export . Copy these and paste them into your game's root directory (e.g., Steam\steamapps\common\City Car Driving ).
Go to Documents\Euro Truck Simulator 2\mod .
Often hosts diverse Russian truck mods for games like City Car Driving.
Use a tool like WinRAR or 7-Zip to unpack the .rar archive.