Answer :

voytek
You can observe this law in practice if a ray of light reflects off of a flat mirror

Law of reflection states that both direction of both incoming and outgoing rays of light make the same angle with respect to surface normal.
The law of reflection are, as follows:

The incident Ray, the reflected Ray and the normal to the reflection surface at the point of the incidence lie in the same plane.

If this does not make since than I hope you know I tried.