External hardware/peripherals are external devices connected to a computer that extend it's functionality. Some common ones are:
1. Monitor - output
2. Keyboard - input
3. Speakers - output
4. Printer - output
5. Microphone - input
6. Mouse - input
Input is anything that's used to feed/put data into a computer. So for a keyboard that's which keys you're pressing, microphone that's sound data etc. Output is any computer-generated data displayed on screen, printed on paper or in machine readable form, such as a disk.
