The Makey Makey is an Arduino (Arduino Sketch editor is C++ code) that connects by USB to a host and is recognized as a keyboard or mouse.
This should help you out:
https://www.sparkfun.com/tutorials/378
If you want to get a joystick, you'd need access to the analog input (pins A0 to A5 are analog) of the Atmel chip on the MaKey MaKey and follow something like this:
http://www.arduino.cc/en/Tutorial/JoyStick.