RC controller transmitter have not really changed much externally over the years in terms of the basic controls. The term "Channels" refer to the number of directional controls on the controller. Quadcopters normally require four channels of control (Throttle, Yaw, Pitch, and Roll). On a four channel transmitter, there are two control sticks, one beside the other, controlled by your left and right hand.
But exactly what the sticks control can vary. These variances can be up to four combinations, called "Modes". But the two most popular modes for quadcopter controllers are Mode 1, and Mode 2. The difference in Modes 1 & 2 are illustrated below.
It is very difficult for the average person to switch between these modes. But Mode 2 is definitely the most popular in quadcopters. The flight tutorials on this site will be illustrated using a Mode 2 controller. Those with Mode 1 controllers can still follow along. But keep in mind that hand movements shown in the videos may be somewhat reversed for your controller.
A gyro stabilized quadcopter can only be controlled to tilt a predetermined maximum tilt in any direction. If you push the cyclic (pitch/roll) controller to its maximum in any direction, the quadcopter will not and can not keep tilting until it flips over. The gyro sensors will prevent that. The maximum deflection that it will tilt varies from quadcopter to quadcopter.
The tilting of the quadcopter is the primary means to control the speed of the quadcopter. The maximum tilt provides the maximum speed it can fly in steady level flight. Some controllers allow you to select varied amounts of that deflection. The varied amounts are called "Rates" and are selectable in terms of the percentage of the maximum rate. For example, indoors it might be better to limit speed of the quadcopter, so selecting a lower rate (say 40%) may be advisable. But outdoors on a breezy day, you may need that speed to fly into the wind. A rate of 80% or maybe even 100% might be needed.
It usually takes the same amount of time for the quadcopter to achieve the maximum tilt of each rate. Thus for a lower rate, the quadcopter will tilt and react slowly. Lower rates are advisable for most beginners, giving the beginner time to react. Tilting reaction at higher rates may be very quick, allowing the quadcopter to turn and stop rapidly. But such rates may be inappropriate for the beginner as it is very easy to overcompensate at higher rates.
When flying your helicopter, you might notice a tendency for it to constantly drift in a particular direction. There are two principal reasons that can cause this. The first is there may be wind pushing the quadcopter in that direction. In that case you'll need to compensate for the wind as you fly by either slightly tilting the cyclic control towards the winds, or pointing the nose of the quadcopter also slightly toward the wind (crabbing).
But another cause may be that the gyro sensor are a little bit off in their understanding of a true level position. Thus they may be constantly compensating (tilting the quadcopter) trying to achieve an incorrect level position. This can be easily corrected through application of the "Trim" buttons on the controller. There normally are four for throttle, yaw, pitch, and roll trim. Throttle and yaw rarely require adjustment. But pitch and roll may need to be corrected after every battery. This depends on if the surface that you're using to initialize the sensors is really level (more on intializing in a later chapter).