up with enough money to pay off your car loan. if the car is worth as much or more than the loan, you can do this when you sell the car because the buyer will give you enough to pay off the loan.
you cannot sell a car that is still under an auto loan, so if the car is not worth enough to cover the loan, you must come up with the cash to cover the rest of what you owe on the loan at the point of sale. 