For example: a computer disk can have a lot of information on it, and the user selects a particular disk for the task in hand. Then the user activates an input procedure to have the computer move a copy of the given required information from the disk, where the original remains, into a part of the computer's memory for further use. The original on the disk can, if desired, be deleted.
For example: Some work has been done using a computer, and now the result is to be moved from the computer onto a disk, which is one of many possible output devices. Usually the computer's screen, which is also an output device, shows exactly what is being done by the user so as to ensure the information concerned ends up at the correct place, outside of the computer. Often a printer is used, which is another output device.