There are normally multiple D-shaped rubber rollers, rotating in feed direction. They push only the top sheet inside the printer where the printer assembly catches it and starts printing. It’s a based on friction feed mechanism. A spring loaded tray always ensure the paper is always touching the roller surface and the roller turns which takes the paper and transfers to subsequent set of rollers / imaging unit.
If printer paper tray is at bottom, load a stack of photo paper into the tray, with the short edge facing toward the product and the print side down. Push the stack into the tray until it stops. For glossy paper, turn the paper so the glossy side faces up. Feed the stack of paper into the paper support. Do not force the paper into the printer. If the stack of paper is too thick to fit, remove a few sheets and try to load it again.
Reference :- Loading Paper and Envelopes