PopSci breaks down how basic functions of R/C work. Once you've mastered it, the sky is the limit. You can remote control anything. Well, almost anything.
"The basic R/C setup consists of a transmitter, a receiver, and several actuators on the receiving end—either servos (electric motors that rotate to a specified position or speed) or relays (which turn electrical components on and off). Commands from the transmitter about position, speed of rotation, or simply "on" and "off" are sent to the onboard receiver, which decodes them into a signal that can be interpreted by the connected servos and switches."
Click through to learn how to make a servo with a little more oomph than your typical hobby store R/C. Also, check out Pop-Sci's R/C creation: the Kamikaze Go-Kart.