Mirrors are used in lasers, fiber optics, and numerous other applications, including the most spectacular success, after initial difficulties, in the Hubbell telescope, which uses a large space-based mirror to show us images from the edge of time. The most recent spectacular failure was the collapse of the Russian space mirror designed to reflect sunlight to the dark cities in Siberia. It fell into the Pacific Ocean. Mirrors occur naturally, as in the reflection of the sun's light on the moon and in the reflections of the sky in the ocean, tuning the water blue. The surface of any still pond reflects images both above and below the water, and the various forms of life in the pond and above it have evolved methods of dealing with the confusion of images created by water bending light.
Mirrors occur in fish scales, butterfly wings, and in eye designs in various forms of life.
They work by reflecting, bending, and amplifying light waves. It sounds very simple, but at least to me, it is not. Symmetry is a peculiar property of nature. Most living beings, amoebae to trees to babies to stars to star fish are symmetrical at least on one axis. The human, like all mammals that I know of, are basically symmetrical or nearly so on the vertical axis.