If the check engine light comes on, then the car should be taken to an auto parts store or automotive service center. They will be able to retrieve the problem code from the car's computer using a handheld device. Most auto part stores will retrieve the code at no charge.
If the check engine light is lit but does not blink, then the issue is relatively minor. It could be due to a loose gas cap or spark plugs that require replacement. However, if the light is blinking, it is an indication of a larger problem, such as a failed ignition coil or fuel injector.
Not diagnosing the underlying problems could impact other parts of the car and lead to an expensive repair bill.