I am not aware of any receipt printers using lasers - thermal printers have an array of resistors that get hot when necessary. I know how a laser printer works and it is hard to explain in 12 or so words. Inkjets are way easier, you can just say "squirt squirt oops". Anyway...

1. A photosensitive drum gets a negative electrostatic charge.
2. A laser shining through a rotating prism scans lines across the drum's surface. This removes charge from parts of the drum that should not be covered in toner.
3. A high-voltage corona wire inside the toner reservoir charges an amount of toner positively.
4. The charged drum rotates past the corona wire, getting covered in toner where its negative charge remains.
5. Paper is pushed against the drum and the powdery toner is transferred to it.
6. The paper continues into a fuser, a little oven where a heating element briefly makes the toner so hot that it melts, its powder particles making a permanent bond among themselves and with the paper. (The heater is usually stationary and heats the paper from below. The fuser drum that pushes paper against the heater can get sticky and pick up some of the toner, making images repeat down the page. This is the most common failure mode that cannot be resolved through regular maintenance such as replacing the toner cartridge and printing cleaning pages. However, almost all laser printers have a cheap fuser module or its drum available so it is usually worth replacing.)