Here's a breakdown:

* Refraction is the bending of light as it passes from one transparent medium to another. This happens because light travels at different speeds in different media.

* When light enters a denser medium (like from air to water), it slows down and bends towards the normal (an imaginary line perpendicular to the surface).

* Conversely, when light enters a less dense medium (like from water to air), it speeds up and bends away from the normal.

The amount of bending depends on the angle at which the light hits the boundary and the difference in the refractive indices of the two media.