Although you already have two answers, I hope to make this one even easier. I'm not sure I even understood the previous answers.

Basically you need 5 channels to control a proper helicopter...

1. throttle
2. elevator (fore-aft cyclic)
3. aileron (left-right cyclic)
4. rudder (tail rotor)
and
5. blade pitch or collective (climb and descend)

From there, the more gadgets you add to the heli, the more channels you will need to control the gadgets...
6. Heading hold gyro with remote gain
7. Governor
8. ect.

Then you have to look at the "features" of the radios. 6 and 7 channel radios have only 3 to 5 points on the throttle and pitch curves. radios with more channels will have 7 or more points on the throttle and pitch curves. The higher end radios will also have additional mixing options, the ability to program switches and set-up the radio the way you want it.

Rafael