What is the difference between a helicopter and an autogyro?

A helicopter gets its lift from the powerplant turning the main rotor. An autogyro's main rotor is unpowered and simply windmills when the aircraft is propelled forward by the propeller. Since this is the case it is not possible for an autogyro to hover for more than a few seconds. Autogyros can takeoff and land in very short distances though, and are capable of very low speeds.

Whereas helicopters are very sophisticated machines and can be very difficult to operate autogyros are much simpler mechanically and are very easy to control as they are inherently stable by design.