You eye works much like a camera. Light rays from something you are looking at enter the eye and pass through a focusing mechanism. The focusing mechanism mostly consists of 2 parts. The first is a "fixed focus" cornea. The second is an "automatic focus" lens. These structures allow for light to be properly focused on the retina, the "film" of the eye. The retina transmits the images formed upon it to the brain so that you are aware of what you are seeing.

Those needing laser vision correction have a cornea which does not have the correct "fixed focus" for proper focusing of incoming light rays onto the retina. In laser vision correction, the shape of the cornea is adjusted so that light is properly focused on the retina resulting in clear images being sent to the brain.