If an insurance company declares your vehicle totalled and you still owe money on it, you will most likely receive enough money to pay it off, but not enough to buy a new car.
The insurance company will compensate you by giving you the amount it would cost you to replace your car. In most states, this includes sales tax and registration fees. The insurance company will subtract your deductibles, if your company is covering the accident.
Losing Your Car
The insurance company will take your car and give you the amount needed to replace it. Then they will sell your damaged car at auction and keep that money.
Keeping Your Car
If you want to keep your car, the insurance company will subtract the amount they think they would have got at auction.
Paying Off Your Car
If you still owe money on your car, you will have to use the money the insurance company gives you to pay off the remaining balance.
If your car was not too badly damaged, you may choose to drive it and live without a car payment. If you want a new car, you basically have to start over and finance a new car.