When light rays hit a mirror, because the surface is smooth and shiny, they are reflected in the same direction, and not scattered at all. As a result, you get a clear image that is an exact copy of the object. The image in a mirror is inverted this means that the left side of your face is the right side of the image.
Most mirrors are flat, but there are convex mirrors make the image seem smaller, so that a larger area can be seen. Concave mirrors, on the other hand, make the image seem larger.