Start by determining what cap you need. Notice the difference in shape.

The type F cap is to be used with aftermarket radiators only. This will not work on an OEM style radiator.

The type D cap is to be used on OEM radiators only. This will not work on aftermarket style radiators.

Installation of both types is the same.

It is important to know that some modern vehicles have a header or expansion tank that holds pressurized coolant. These tanks usually house the radiator cap (instead of being on the actual radiator) and can use different style caps. For example, the 2017+ Civic Type-R uses an expansion tank and requires a Type-F cap.