Think of a microprocessor like your brain. Your brain connects to your body's senses - sight, touch, smell, taste, and hearing. A microprocessor connects to sensors that allow it to see or hear things.
If your brain sensed a ball coming at you, it would make you move out of the way. Like your brain, a microprocessor can also make choices based on the information it receives. The received data is called input.
Your brain might send a signal to your body that has information about how to move. A microprocessor can also send a signal to a motor to move. The transmitted data is called output.
Receiving input and output allows your brain and a microprocessor to do things. A microprocessor's way of thinking is its program. The program can tell the microprocessor what it should do when something happens.