Auctions are pretty much the only places that can sell a totaled car. Insurance companies take vehicles that have been declared a total loss and sell them to get back as much money as they can. They have specific auction houses they deal with and, in the majority of states, the public is not allowed to bid on these vehicles. Auto dealers and other industry professionals that have an auto brokers license are the only allowed bidders. The majority of totaled cars are sold to salvage yards which strip them of the valuable parts. If your car is totaled you may be able to work out a deal with the insurance company to keep it if you want to repair it yourself.
For more info, see What Is a Salvage Title?