What does prism?

A prism can help us understand the refraction and the reflection of light when it asses between 2 different mediums ( from one medium into another less refractive or from one medium into another more refractive ) and the ray of light may emerge out of the prism by refraction or by reflection and sometimes by total internal reflection ( by obeying the 2 laws of reflection and by making the angel of incidence equal to the angle of reflection ) and sometimes it may continue its path without deviation that is when the angle of incidence is equal to 0 degrees then the angle of refraction will be equal to 0 degrees this is called undeviated !

It separates the wavelengths contained in a beam of light.