Here’s one with an outside view, which I think is easier to grasp for non-pilots: https://youtu.be/twGid07JR9s

Basically, the helicopter “falls” down and slightly forward, driving the main rotor disc (potential energy turning into disc rotational energy), then the pilot flares the helo, slowing the forward speed and taking energy from the rotor disc to slow the vertical descent, finally resulting in the aircraft settling to the Earth at a slow speed. Just like gliding an airplane, it’s a one-shot kind of a thing (except in training where you generally keep the engine running and available).

Note that the rotor disc is connected to the engine via a one-way clutch, so the engine can drive the rotor but not vice-versa. Otherwise, a seized engine would result in a rotor disc stoppage (and an uncontrolled descent).

https://www.youtube.com/watch?v=BTqu9iMiPIU&feature=youtu.be...