What is the difference between an input and output device?
An input device sends information to a computer system for processing, and an output device reproduces or displays the results of that processing. Depending on the interaction, a device can be both; referred to as an input/output or I/O device.
For example, as you can see in the image, a keyboard sends electrical signals (input). Those signals are then interpreted by your computer, and then displayed on a monitor as text (output). Then in the lower half, you can see a computer sending data to a printer that will be reproduced on a piece of paper (output).