A car is in a serious accident. Maybe it was a multi-vehicle collision, maybe the car met a hazard in the road, or perhaps the car was safely parked and ran afoul of falling debris, unusual weather or a careless snow plow blade. Regardless, the police, the tow truck and the insurance agent are all duly notified and it's time for an army of professionals, from auto service technicians to an auto body estimator to see what can be done.
If there's too much structural damage to the car, it may simply be a write off. In these cases it would be impossible to render the car road safe again or the cost of repairs far exceeds the remaining value of the vehicle. Sometimes, in the latter case, a car owner may feel sentimental enough to try to salvage their car but usually there's nothing left to do but to send the wreck to the junk yard to be stripped for parts and then compress it.
Insurance companies will also decide what should and should not be fixed. They will also pursue the person responsible for the accident for damages, though as every driver is legally required to carry insurance and this includes liability coverage, if two people are in an accident it will almost always be a negotiation between the insurance companies. If the other party was uninsured, the insurance company may even pursue legal action after them directly. This is also the case if say, a negligently maintained property collapses onto a car.
Even if the car is still driveable, a thorough inspection is a sensible response after anything other than a scratched paint job. Road worthiness is controlled by strict regulation. Small problems may leave a car driveable, but put drivers and passengers at risk if there was a second accident. Alternatively it may be a matter of hidden structural integrity problems. Reputable auto mechanic programs give their graduates the certification they need to do wreck assessment.
To greatly simplify the inspection process, someone, or often several people with auto technician training will assess the engine, body, frame and additional features like the tires. A cracked frame can be a disaster for a car. If there was serious skidding, tires may need to be changed, and a deployed airbag always has to be replaced as they explosively inflate and are single use only. Small damage like chips to the windshield may be fixed, but cracks usually require replacing the entire thing.
Modern car bodies are fiberglass shells. A seamless looking patch has to be sanded level with the rest of the car's body, and painting in itself can be very expensive for perfect looking results. One of the reasons most cars have gloss rather than matte finishes are because upkeep is easier.
