The size of a wave depends on its fetch. The fetch is the distance a wave travels. The greater the fetch, the larger the wave. Wind speed also has a significant effect on the size of waves. The stronger the wind the larger the wave. Finally, wind duration also affects the size of a wave. The longer wind blows over the sea or ocean the larger the wave.
As a wave approaches a beach it slows. This is the result of friction between the water and the beach. This causes a wave to break.