What is dispersion, and how is it related to diffraction and refraction?

Refraction is simply the bending of light when it moves from one material into another. If light is beamed at 90° to a surface, no bending happens. But if you shine the light at an angle it will bend one way or another.

Diffraction is a process in which a beam of light travels through a gap or around a barrier, and spreads out as a result.

Dispersion is the property that the speed of light in a transparent material is different for different wavelengths. Thus the index of refraction is likewise different.