It basically means this
•The ray of light which strikes the surface is called the incident ray.
•The ray of light which leaves the surface is called the reflected ray.
•A line perpendicular to the surface is imagined at the point of reflection. This line is called a normal. In this context the word normal means perpendicular.
•The angle between the incident ray and the normal is called the angle of incidence, or the incident angle.
•The angle between the reflected ray and the normal is called the angle of reflection, or the reflected angle.
Notice that the angle of incidence is = to the angle of reflection.
There is this website - click here - that shows how a light beam reflects at the surface of a flat mirror. It is an animation. Simple, but it may explain it to you. Scroll down the website and you'll see the animation.
Have fun!
