The best way to understand the way the eye works is to think of the eye like a camera. The part of the eye which senses the light is the retina and that is a thin layer of nerve cells at the very back of the eye.
To see clearly, we have to have an in-focus image
But in order to see clearly, we have to have an in-focus image and that is where the cornea and the lens of the eye come in.
The cornea of the eye is the front window of the eye, and this does two thirds of the focusing of the light onto the retina.
The final one third of the focusing, and also the zooming mechanism of the eye, are performed by the lens which is inside the eye. This lens is capable of moving and focusing at different distances and fine tuning the sharpness of the image onto the surface of the retina.