What part can be found on a camera an eye and a pair of glasses what does this part do?

This part is called a Lens, on the camera and the glasses the are made of either optical glass or optical plastic, in the eye the lens in an organic material.

Lens allow light to enter the camera, eye or glasses, and focuses that light on a surface such as the camera's film, the eye's retina, and the glasses wearer's eyes.