It's stored and then formatted depending on the lasers page language. Once enough data has arrived to complete a page, the laser printer starts a series of things happening. First it starts to send the page to the drum, Line by line. A laser beam is modulated to place dots on a rotating drum, one line at a time. Above in our graphic, you'll see the laser hitting a mirror that directs the beam onto the drum surface.
Many laser printers use different types of drums.
The drums are charged to be either negative or positive depending on the model. As the drum rotates it touches a roller called the developer roller. Some people call them Mag rollers. The Purpose of the roller is to pickup toner from the toner chamber, then with an even layer of it, roll on to the drum. The Roller is charged with either positive or negative voltage.