Mirrors are very smooth and shiny.
Light bounces, or reflects, off of the smooth and shiny surface of mirrors. When you see your face in a mirror you are seeing light from your face reflecting off of the mirror. Light bounces off mirrors very much like a bouncing ball. You can throw a ball straight down, and it will bounce straight back at you. Or you can bounce a ball at an angle and it will bounce off the floor at the same angle away from you.