i don't understand what it is. help me

Either you mean POV-Ray, or you mean the raytracing option in setup. The first one makes pretty pictures, the other makes the game prettier.

If the second one doesn't work on your computer, you can read here to find out why.

For an actual explanation:
http://en.wikipedia.org/wiki/Ray_tracing_(graphics)

For an ingame comparison:


Raytracing makes your tori have reflections and makes him shiny.

It's just a graphics option that makes you look cooler.
Some items called chrome give a ray-tracing effect without the option being ticked but they are rare and high priced.