Inputs are anything that you pit into a system. For a computer the input can be from the user via a keyboard or gaming controller, you can also get input from usb sticks or cd's essentially anything that goes into your computer or system.
The process is what the system does with these inputs. Again with the computer example it takes in what you press on the keyboard or joystick to say controll an action in the game.
Output is anything that kinda like goes out of the system. For example your computer monitior is an output device and so are stuff like speakers, printer a usb stick can also be an output device if you put something on it essentially anything that goes out of the system.