Answer:
It accepts data, pixel information, millions of it. Input.
It displays data through the LCD. output.
Heck, it has its own processor. It's a computer by itself!
Then, if you connect it to a computer with a USB cable, it transforms to a mere storage device. Surprised? Connect one and check My Computer. The camera appears there as a Removable Storage Device or something to the tune of that. It's no longer a camera when that happens. It's only one big expensive card reader.