The wind causes waves on the surface of the ocean. Stronger winds, like in a storm, make larger waves. Why don't you try and make your own waves, by blowing across the surface of a full bucket of water.

Waves of water move up and down. You can easily tell this by watching a floating boat bob up and down with a wave.

Tsunamis are different from the waves I have described, which are caused by the wind. Tsunamis are very big waves usually caused by underwater earthquakes, volcanic eruptions or landslides. It will be like if you dropped the full bucket of water and then you will see that it will cause a big wave and the water will probably splash out on to the floor causing a big mess. Oh dear!