The refraction of light is the bending of the light rays as they pass from one medium to another. Refraction happens due to a change in the speed of the light ray or wave. This change of speed is characterized by the index of refraction.
The Snell’s Law quantitatively defines the amount of bending of waves, depending on the refractive index of the two media. In the cases where we have a large incidence angle and the Snell’s Law doesn’t have a solution, we get total internal reflection and refraction won’t happen.
The Fresnel equations describes the amount of light being refracted.