There are so many laser printer parts inside your printer, the toner cartridge has two main components, one is the drum and the another is hopper. The drum begins to turn around when the printer starts to run, its surface charges with negative electricity from a charge roller. The drum has a layer of sensitive coating on the surface, it gets hit by laser beam and as it turns. As the laser radiates the drum line by line for million times per second, it releases the electricity to create more non-electricity spaces, until they finally form an same image as the document right on the drum, just outside the hopper, there's a roller that gets covered with toner particles as the drum turns past this roller, the toner has no choice since the toner carries a negative electricity to be attracted to the non-electricity spaces on the drum, at the same time, the toner is repulsed by the negative electricity that cover the rest of the drum, so the toner only sticks to the spaces hit by the l...