What happens when you drive someone elses car
To drive someone elses car could be a very nice time and easy solution when you need a car, but you do need to understand how your insurance works when using other cars than your own. The U.S insurance is most likely to follow the car. That means if you would have an accident whit someone elses car, its most likley that their insurance coverage that would pay for the damages or injuries. But there is some things that you need to know.
If the owners insurance includes permissive use, it means that they have given you the permission to drive their car. It would most likely approve you as a temporary driver if they have the permissive use as a part of their policy. But the other way around, if they dont have that part of the policy, if it dosent include permissive use, their insurance is most likely not covering you.

Would the damages from an accident, go over the limits for the owners insurance., then your insurance is going in to cover the remaining costs. This is something that works specially whit liability coverage, its going to help you pay for any damages or injuries.
You should also know that some of the policies dont have the cover of certain types of drivers, it could be limits due to certain ages or drivers whit a poor driving history. So before you go about to borrow someones car, it could be a good idea to check their insurance policy so it also would cover you in case of accidents.
As a summary, the car owners insurance would cover you most of the times, but it could be a good thing to check their policy so you dont ends up whit trouble on your hands.