FP v. CP Helicopter Control

To control a helicopter the pitch angle of the main rotor blades must be changed in relation to the air flowing over them. This change varies the amount of lift generated by the blades.
Pitch angle is referred to as Angle of Attack when the blade is moving through the air.

Main rotor blade control comes in two forms, cyclic and collective.
Cyclic controls directional movement of the helicopter (left, right, back and forward) whilst collective controls altitude (up, down).

Cyclic control changes the pitch angle of the whole rotor disc, which is the imaginary circle drawn in the air by the tips of the spinning blades. Imagine a dinner plate spinning round on a pole, and tilting up and down slightly as it spins - this is effectively what the rotor disc does when cyclic control is applied.