Assum that you mean helicopter, a helicopter flies because the rotor blades are basically spinning aerofoils, providing Lift. As the helicopter moves forward you get asymmetric lift. This is countered by lowering the forward moving blades AOT the tail rotor is there to stop the craft from yawing wildly as a counter reaction to the spinning rotor. Of course, it is a bit more complicated than that.
Do you mean "How does a helicopter work" ?