Visible Light is a form of electromagnetic radiation from 400 nm to 780 nm and has properties of both a wave and of particles, which is why there exists a wave-particle duality and quantum theory.  Light is the fastest moving thing at about 300,000,000 m/s (186,000 mph).  Lenses cause light to refract since it changes the speed of the light when it is inside of the lens.  The change in the speed light is based on the index of refraction of the substance, and a higher number causes more refraction.  Mirrors on the other hand, cause the light to reflect.  Lenses and curved mirrors have similar properties when it comes to forming images since focal points occur in both.  Depending on where the image is in relation to the focal point, different phenomenon occur which might create a real or virtual image that can be larger, smaller, or the same size as the original image.