Early lithographers etched images onto flat stone. These images would accept ink, while the porous stone accepted water. When ink was applied, it stayed on the greasy image area and avoided the rest of the stone.
Modern lithography uses the same concept but adds one important element.
In modern presses, the image is transferred from the printing plate to a rubber blanket and then to the paper. Although there are many different kinds, sizes and qualities of offset presses, the basic configuration remains the same. When the printing plate is exposed, an ink-receptive coating is activated at the image area. On the press, the plate is dampened, first by water rollers, then by ink rollers. Ink adheres to the image area and water to the non-image area.