To add coolant to a car, open the hood, and remove the cap on the white plastic tank that is next to the radiator. Add a 1:1 mixture of coolant and water up to the full mark, and replace the cap.
Ensure that the car is in park and the engine is cool before opening the reservoir. If the engine is hot, the pressure from the system could cause hot coolant to spray out. Car owners can purchase concentrated coolant and mix it with distilled water or purchase premixed coolant. Premixed coolant is often more expensive, but it is less messy and more convenient to use, especially for a quick topping off.