Optics is the physics of light. It describes, alongside other phenomena, how light can be reflected by mirrors, and bent (refracted) by materials like glass or water.
This site tries to explain some of the various aspect of optics, and each explanation is accompanied by a simulation. All of the simulations are interactive. Try playing with the one to the right, which has a laser beam, glass, and water.
After that, you can move on to reflection, or skip straight ahead to refraction.