The scanner is a piece of technology which unlike the printer is an input device which basically scans the top-view of any flat surface (usually paper but is definitely not limited to it) introduced in its effective range using light. The data scanned is then transfered to the Central Processing Unit for futher processing. The processed image can then be outputted and seen on the monitor's display. Once available for printing, the Central Processing Unit will just send the processed image into the printer ad voila, your scanned image is now printed in a piece of paper!
Today, scanners come with printers as a bundle. It is a perfect combination since the printer will just print the image anyway.
