The easiest method is purchasing via . When you buy "City Car Driving" on Steam, you never see a serial number. Steam automatically ties the license to your account. This is the safest method.
The keyword focuses on the , meaning you are looking for a personal, non-commercial license. city car driving serial number home edition
While the serial number is your proof of purchase, the game also generates a "Product Code" (or Program Code) specific to your hardware. You use both to generate an "Activation Key" on the official activation page . The easiest method is purchasing via