As the name shows, inkjet printer jets ink out to print onto media, normally paper.
Before printing, the file has been translated into dots to make up the image of the file, and then sent to printer.
During printing, ink is emitted from nozzles, which are located on print head. The print head move from left to right and back horizontally, and paper moves vertically one-way from back to front or front to back.
There are two major types of technologies to get ink jetted out from print head onto paper.
One is thermal technology, most inkjets use this method to print. When printing, ink droplet is heated, it expands then bursts. This causes the ink squirt through nozzles onto paper. The inkjet printers, made by HP and Canon, employ this technology.
The other method is used by Epson ink printer, and called Piezo-Electric technology. Epson ink printer uses a Piezo crystal at the rear of the ink reservoir. When printing, a current is applied to the Piezo element, then it flexes, and forces ink droplet out of the nozzle.
The dots, created by ink, will show on paper, by now the file has been printed.