I will probably go with FM for any future radios as I think it offers the best value for my dollar. The servos are little motor driven devices which convert the radio signal to a physical movement. They have output shafts to which an arm or wheel can be attached. When the receiver tells the servo to move the output shaft rotates which causes the arm to swing or the wheel to turn. We can then connect the arm or wheel to a pushrod or cable which in turn is connected to the function we need to opereate, such as the throttle.
Servos come in different sizes and strenghs.
A very strong servo might be used for flaps or landing gear whereas a simple, lightweight servo might be used for throttle. The batteries most used for powering radio controlled aircraft are Nickel Cadmium or NiCad batteries. They come in many different sizes and capacities and can be recharged over and over again. The most common size for airplanes is a 500 mAh, 4.8 volt battery. Helicopters usually have a 1000 mAh battery because of the extra demands of 5 servos and a gyro.