The shape of your eye influences how well you can focus on an object. Light rays enter the eye through the cornea. When light strikes the cornea, it bends, or refracts the incoming light. The light then passes through the lens which further refocuses that light onto the retina, a layer of light sensing cells lining the back of the eye. The retina begins to translate the light into what you see.
For you to see clearly, light rays must be focused by the cornea and lens to fall precisely on the retina. The retina converts the light rays into impulses that are sent through the optic nerve to the brain, which interprets them as images.
The refractive process is similar to the way a camera takes a picture. The cornea and lens in the eye act as the camera lens. The retina is similar to the film. If the image is not focused properly, the film, or retina, receives a blurry image.