These two devices allow you to control a quadcopter wirelessly. The transmitter is the device you hold in your hands and it sends data to the receiver. The receiver then hands off that data to the Arduino for processing. 

 

Transmitters look really complicated at first, however they are pretty easy to understand. 

Here is an example setup. In this picture you can also see the three axises that the gyroscope will read data from. 

 

Flying a drone is really difficult however it could be easier using an auto-leveling program.

This will keep the drone perfectly stable if you take your hands off of the controller.