Group theory, dihedral group Why we study dihedral group? Please tell Real life example of dihedral group. I know this group mathematically.

From the comments: Actually I am going to tell about dihedral group to friends. So in introduction to dihedral group I have to tell the use of dihedral group in practicle life.why we need dihedral group. From where this originate.

The first (as in at an earliest age) example of a dihedral group in action that most of your friends have seen is the kaleidoscope.
There the viewer sees a pattern $P$, its reflected image, the reflection of the reflection et cetera. Altogether the view consists of parts like $g(P)$, where $g$ ranges over a dihedral group. Or a bigger group - all depending on how many mirrors are used (with two mirrors you get the dihedral group).
