Waves are caused by energy. There is a push on one side and a pull on the other. The most common type of wave is in the ocean. The wind blows the water causing friction with one side rising and the other falling. The stronger the wind, the greater the friction and the bigger the wave will be. This is why hurricanes will create tsunamis. Waves so big and powerful that it will destroy giant cities.
What other types of waves are there?
Heatwaves, radio waves, microwaves, hair waves, internet waves
The same rules apply to making all waves.
Waves are caused by an external energy that goes against the grain.