The Hold switch will take the engine to an idle position on the throttle and hold it there. By doing this the engine will still stay running but will let you have control of the collective pitch so you can practice your autorotations with the helicopter. The typical pitch settings will be about a minus 4 degrees to a positive 10 degrees. Both the top end pitch and low end pitch will very during test and set up of the helicopter.
Another two features the radio will most likely have is two knobs that will be called "Hovering Pitch" and "Hovering Throttle". What the hovering pitch knob will do is very the amount of pitch you have at you set hovering stick position. example would be if you hover at 1/2 stick position and at that position you had a positive 5 degrees pitch. When you vary this knob you might get lets say 4 degrees to 6 degrees of pitch. This will fine tune your helicopter so it will hover at exactly 1/2 stick position. The hovering throttle knob will do the same as the hovering pitch knob but it will do it only to the throttle. It will vary the throttle position or fine tune it at the 1/2 throttle position or where ever you have set that hover position to be. Yes there are some radios that will let you dictate where you want to hover at. Some people will set up for 3-D aerobatics by hovering at 3/4 stick. This will let them also hover inverted at the 1/4 stick position. By doing this the pitch and throttle curves stay more linear.

For all the above it is what every pitch will hover with not to much or to little rpm in the head. This is typically at +4 1/2 to 5 degrees of main blade pitch. Typically about 1550 - 1600 rpms is about normal. If it gets to slow the helicopter will be sluggish and you can get in trouble with it in the wind. If its to fast it becomes touchy and will be hard to control.
* These are just some typical set ups. They will very between pilots. These will only get you started. If you don't use any negative pitch to start you end up with a helicopter that is like one with fixed pitch. And if you learn with what you will have later or close than the transition will not be a big thing later.

Terminology

Autorotation - This is the term for when the engine is either not running or is put into a idle position with the "Hold" switch.

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