By changing the shape of the lens you change the angle of refraction of the light passing through the lens and thus move the point of focus closer to or further away from the lens.
(you; change; the angle of refraction of the light) (the light; passing; through the lens) (you; move; the point of focus closer to or further away from the lens)
you the light you
change passing move
the angle of refraction of the light
through the lens
the point of focus closer to or further away from the lens