An IR transmitter -- your TV remote or your RC helicopter controller -- sends out pulses of infrared light via an LED on the transmitter in a code that the IR receiver interprets and turns into specific commands such as Volume Up/Down (your TV) or Turn Left/Right (your RC helicopter).
The range of an IR signal is usually limited to around 30 feet or less. Infrared also requires line-of-sight, that is, the LED on the IR transmitter must be pointing at the IR receiver in order to work. It doesn't see through walls.
With or without infrared navigation, IR can add another element of fun to RC vehicles. There are RC tanks and RC airplanes that can fire at one another using infrared -- a hit might result in sound effects or a temporary disabling of the opponent.