Collective pitch is where the pitch of the main rotor blades may be simultaneously increased or decreased to change the amount of lift. This gives a quicker response to changes in vertical thrust as controlled by the pilot. The reaction time is longer and thus the control is less responsive. There is a trade-off, however, and that is the cost and complexity of the rotor head. There are a great deal more moving parts in a collective pitch rotor head and thus, they are more expensive.
Most current choppers are of the collective pitch variety.
On a standard, collective pitch helicopter there are four controls and these are operated by five channels of your radio system. These controls are the collective pitch, the fore and aft cyclic pitch, the side to side cyclic pitch, and the tail rotor pitch. The collective pitch must also be coupled with the throttle of the engine so that when more load is put on the main rotor blades by increasing the pitch, more throttle is applied to help overcome the additional drag. The left stick of your radio transmitter controls the collective and throttle in the vertical direction and the tail rotor pitch in the side to side direction. The engine of a helicopter drives both the main rotor shaft and the tail rotor via a series of gears and a clutch.