I'm no expert but here goes: If you fly a collective pitch helicopter you know about "autorotation," the emergency procedure used if the engine quits. You dive and build rotor speed using forward cyclic and negative pitch then pull out and flare into a (hopefully) safe landing with rear cyclic and positive collective.

An autogyro flies using negative (or very little positive) incidence in the blades to keep the rotor spinning and uses the engine's power to create forward motion of the aircraft and the constant spinning of the blades creates lift as the air flows through them. Well that didn't come out exactly right but I'm sure the experts will sort me out!
Oh, read and absorb this: http://www.autogyro.com/ There will be a test at 9:00!