If you drive your parents' car with their permission, their insurance usually covers you. Car insurance is mainly for the car, not specifically for the person driving it.
However, some insurance policies may have a limit on how frequently a car can be borrowed. For example, you might be allowed to drive your parents' car up to 12 times a year without being listed on their policy.
So, if you plan to drive their car regularly, it's best to get added to their insurance. This way, you'll always be protected.