If you are not at fault, you have two options. You can contact the insurance company of the person who is at fault for the accident, who will pay for the damage to your car only if they determine that their insured caused the accident.
In the alternative, if you purchased collision coverage, you can contact your own insurance company who will pay for the damage to your car, less any deductibles, no matter who is at fault for the accident.
Once you decide how to proceed, the insurance company will send an adjuster to estimate the damage. The insurance company is responsible for paying the amount it costs to fix the car or the fair market value of the car, whichever is less.