The radio system is to connect between you and your model rc toys (remote control toys) such as rc car, rc helicopter, nitro rc car, rc gas boat, remote control helicopter, remote control car etc.. It looks like a bit complicated at the very beginning but with some study, all aspects of the radio system can be easily understood. We will introduce you to the radio system here and explain a few of the features found on many of the systems available today.

Radios are separated into two groups, those used for model aircraft and those used for
surface models. Although the operation, electronics, and mechanics for both types of systems are virtually identical, they operate on different sets of frequencies. The separation is stipulated by law and it is to protect the safety of the modeler and those in the vicinity.
A flying aircraft can be dangerous if it becomes uncontrolled and the frequency separation helps avoid an aircraft being interfered with by someone operating a car or boat. In addition to a difference in frequencies, some surface radios are also available as a pistol grip control which is ergonomically easier when controlling cars and boats. A pistol grip for aircraft would be impractical.
The first criteria one usually looks for when choosing a radio is the number of control functions or channels. (Note that the term channels here refers to the number of controls and does not have anything to do with the frequency on which the radio operates.) Generally modern radio systems are available with anything from 2 to 10 channels.

What comes with the radio
Transmitter: The transmitter is the control box which you hold that converts your human control movements into electrical impulses and sends them via radio waves to the receiver in your model.
Receiver: The receiver is the small electronic unit in your model which converts the radio signal from your transmitter into electrical control signals which can be sent to your servos.
Servos: Servos are the devices in the model which actually produce the control movements. They convert the electrical signals from your receiver into physical movement to control your model. A different servo is required for each control function or radio channel.
Batteries: Virtually all 4-channel and greater systems come complete with rechargeable NiCd
battery packs for both receiver and transmitter.
Dual Charger: A dual charger will come with any system that is complete with NiCd batteries.
It will charge both the receiver pack and the transmitter pack at the same time. Switch Harness: A switch harness is provided to turn off the power to the receiver and servos in the model. It goes between the battery pack and receiver and also has a lead for charging.
Servo Accessories: Most radio systems will come with additional servo arms and hardware for mounting them.
P.S. Common rc toys (remote control toys) and hobby items: rc car, rc helicopter, nitro rc car, rc gas boat, remote control helicopter, remote control car etc.