Normally your liability insurance will not follow you when you are driving another person's vehicle, but in some cases it is used as secondary or excess insurance. Of course your property damage liability insurance would not cover the car that you were driving but in some situations it could cover any vehicles or property that you damaged when operating your friend's car.
Usually the primary insurance would be that on the vehicle by the owner and thus used first if you had an accident in a friend's car. Then if their insurance limits were reached your insurance as the driver would be used.
Insurance company guidelines and state laws can differ though so check with your insurance provider to make sure your liability insurance follows you when you drive another person's vehicle. And if you plan on borrowing a friend's car, they may want to check and make sure their insurance would cover you as the primary insurance when you are operating their vehicle.