What causes waves?

Waves are most commonly caused by wind. Wind-driven waves, or surface waves, are created by the friction between wind and surface water. As wind blows across the surface of the ocean or a lake, the continual disturbance creates a wave crest.

Does this mean, winds are stronger in seas where one can surf?

The warmer, less dense air above the land rises, pulling in, the more dense air from out to sea to replace it. Subsequently, the wind switches and turns onshore. So it is usually the case that the best winds for surfing are offshore winds, which more frequently occur in the mornings.