The answer is essentially what has already been said. Light waves, like radio waves, are just electromagnetic radiation, classified according to their frequency (or wavelength). The general idea of transmitting information is fairly simple. You have a transmitter, which takes some signal, such as a sound or an image for example, and encondes it into a specific sine wave which is transmitted through the air. Your reciever is generally tuned to look for specific frequencies, which it picks up and decodes back into the original information (sound or image, for instance). Both transmitter and reciever are typically what you see everyday as antennas.
The information is encoded in various ways, as was already mentioned. AM is amplitude modulation, where you change the amplitude (you can sort of think of this as the "volume" or "brightness" of the wave). FM is frequency modualation, where you just slightly modulate the frequency. There are other ways to do it too, such as PM or pulse modulation where you basically turn the signal on and off. When you really think about it, these modulations in the signal are no different than the simple examples of morse code or the traffic light already used. There is a kind of "key" by which you can encode and decode the signals, and this is done through various kinds of electronic circuits, the design of which is considerably more complex than could be described here.
