Waves are formed as a result of wind blowing across the top of water. In general, the stronger the wind, the bigger the wave, although the angle and duration of wind also affects the strength of the wave.
In addition to being formed by wind, waves can also be formed as a result of a physical object. If something is dropped in a liquid, or propelled through, like a boat, waves form. Overall, the amount and size of waves caused by physical objects are insignificant compared to those caused by wind. Depending on the size of a wave, it can be classified as a capillary wave, wind wave or other type of wave.