Each nozzle is responsible for spraying one dot of ink in a particular position. The print head, consisting of up to 128 nozzles moves horizontally across the page as the paper is fed through the printer. Ink is typically fed to the printer by inserting small cartridges filled with ink, not unlike a miniature version of an old fashioned stamp pad. By adding the capability to deal with multiple cartridges containing different colored inks, many manufacturers were able to start offering relatively inexpensive color inkjet printers. If you want to use the same printer to output full-page graphics and photographs, you may find it isn't well equipped to do so.
Laser printers work on a different principle which is similar to a photocopying machine.
It involves using a high voltage corotron to ionize a rotating drum which is then exposed to a laser to etch away the charge in the spots that are meant to attract ink. The areas of the drum that were etched by the laser then attract particles of black toner, forming the image of the page on the surface of the drum itself. A sheet of paper is then charged by another corotron and passed in close proximity to the drum. This transfers the image of the page from the drum to the paper. The paper is then de-charged by yet another corotron, and the image is fused or sealed onto the paper by the application of heat at around 400 degrees which melts the toner onto the surface of the paper.