Snell's law describes how the angle of refraction of a ray of light varies with the angle of incidence when light passes from one medium (e.g. air) into another (e.g. glass).
The video below demonstrates a simple experiment which may be performed to investigate Snell's law. In the experiment a semicircular glass block is placed on top of a calibrated piece of paper so that the various angles may be measured. (The quality of the video may limit the precision to which the angle of refraction may be measured).