Double pole breakers can channel 240 volts instead of the normal 120, and 20-60 amps instead of the normal 15-20. They also have two hot wires connected to one neutral wire, unlike single pole breakers, which have one. If either hot wire experiences a short, both of the poles will trip.
Because they provide more energy, they're necessary for some larger appliances, like car chargers, dryers, central air conditioners, and some stoves and water heaters. They can also be used as two 120 volt breakers, and can still provide power to smaller appliances as well.
Although it's a more advanced project, you can install a double pole breaker yourself. This procedure may require a special permit, and some municipalities require these systems to be inspected by a certified professional.