For GCSE biology you will need to learn a diagram of the eye and the main points, which include:

Retina - has rods which detect brightness and cones which detect colour.

Yellow spot - when you focus on an object, this is where the image falls. It is highly concentrated with rods and cones.

Blind spot - where the optic nerve leaves - there are no rods or cones so you can't see this point.

Optic nerve - takes impulses to the brain.

Cornea - protects the eye and also starts bending the light.

Pupil - small in bright light and large in dim. Controlled by muscles in the iris. This protects the retina from very bright light which could damage it.

Lens - bends the light and turns it upside down so it can be focused on the retina.