Light consists of rays that enable us to see something. For example, light rays fall on an object, which sends part of the light rays back again. These light rays then contain important information about the colour, the shape of the object and where exactly it is. Our eyes pick up the light rays and pass them on to the brain. Only then can we see the object.
Without light, we can't see anything at all. Or to put it the other way round: the more light rays that fall into our eyes, the better we can see. Light rays are straight. When they hit an object, they are either absorbed, i.e. retained, or reflected, i.e. diverted in another direction. Dark colours can swallow light, light colours reflect more.
Light rays come from light sources. The brightest light source we know is the sun. It consists of the gases hydrogen and helium and shines so strongly because hydrogen atoms constantly combine to form helium atoms. This produces light and heat.
Until modern times, people did not know exactly what light was. They thought, for example, that we see by rays coming out of our eyes. These rays scan things and go back into the eyes.