Solar sailing is a way of moving around in space by allowing sunlight to push a spacecraft. In everyday experience, we do not feel any kind of force or pressure from sunlight. This is because sunlight is so gentle that all the other things in our environment - gravity, wind, and the strength of our own bodies - drown it out. However, in space, there is no air, and objects are freely falling through space instead of constantly fighting gravity. In this environment, sunlight can dominate and allow spacecraft to move at will, like sailing vessels on Earth's oceans.
The following documents describe the basic principles of solar sailing.