Photography without light is like fishing without water—relatively pointless.
Light sources emit visible and invisible rays, and objects reflect a percentage of these rays back. A specially shaped piece of glass bundles parts of this light and projects an image onto grains of silver salts, triggering a chemical process that causes them to change and turn black in the exposed areas.
Without light, we would not be able to take photos. Light is technically necessary, but can also be used creatively. Light has direction, intensity, and color temperature. It can be emitted by a point or area source of light.
In school, you probably learned ...