Lenses are used in many optical devices like microscopes, telescopes, cameras, and projectors to refract light in a way that magnifies or projects images. There are two main types of lenses - convex lenses that converge light and concave lenses that diverge light. Lenses work by refracting light as they are made of curved surfaces of glass or other transparent materials that act like segments of a sphere or combination of prisms to bend light rays.