If you mix the 3 answers given you might be able to understand what an "auto" is.

1. No need to shut down or kill the engine. There is a function on most radio controllers to bring the engine to IDLE and leave it there, not reacting to what the throttle stick is doing. Remeber that the throttle stick on the radio is shared by the pitch function.

2. The angle of the blades is decreased to something less than zero degrees. Is actually closer to -4 degrees. Zero degrees will not create enough energy on the blades to perform a successful flare and landing.

So let's review;

1. You intentionally flip your Throttle HOLD switch on your radio (bring engine to IDLE) or your engine dies (emergency auto).
2. Inmediately bring the pitch stick down to about -4 degrees. Some people prefer even more blade deflection. I use close to -10.
3. As the heli drops to the ground, the air passing thru the rotor disk, maintains or increases the rotational energy of the blades.
4. As you approach the ground, (no set altitude as all helis are different) you increase the blade pitch back to a little over hover deflection and "arrest" the fall, and any forward movement. This is called the FLARE.
5. If you did it right, you should have enough energy left in the blades to settle softly to the ground. (Landing)

Rafael