Question

What are flat mirrors used for?

Answer 1

Well, basically, to reflect light and also create a virtual image.

Explanation:

A flat mirror can be used to redirect light and in doing so change the direction of a light beam. In many devices you use flat mirrors to "move"a light beam where you want:

Also when you want to get dressed and see the end result you use a flat mirror to "see" yourself reflected as a virtual image in it.