Where to begin?
There are two major forces involved in the creation of a wave: wind and gravity. As you may already know, the moon’s (and, to some extent, the sun’s) gravity effects the tide, which contributes significantly to building waves. Between the wind and the tide, sea water can get moving pretty fast.
But just because water is moving does not necessarily mean that a wave will form. For instance, river water moves very quickly but it does not crest like an ocean wave. Something else causes the waves to crest.
Think garden hose.
When a set moves closer to shore, the amplitude of each wave increases (the waves get bigger). As the water gets shallower, there is less room for all of the fast-moving water to occupy, so it goes the only place it can: up. This is why waves look smaller when they are far out.
If you’ve ever covered the end of a garden hose, you’re familiar with this effect already. The rate of water leaving the hose has to remain constant. However, there is less space for the water to occupy, so it exits much more quickly to make way for the traffic jam behind it.
The water that rises due to crowding needs somewhere to go, and fast, so it goes up, and fast. The rising water moves faster than the water in front of it, so the wave eventually gets too high and breaks. So when you’re riding a wave, you’re riding water that has no option but to push you forward quickly.
Occasionally, you might notice two waves colliding. Depending on the alignment of the crest of the wave, the two waves will merge into bigger, smaller, or similarly sized waves. Those who have studied physics understand this phenomenon, called interference. If the crests of each wave align, then the constructive interference results in a much larger wave. If the crests do not align, the destructive interference results in a smaller wave.
To put it simply, experienced surfers dig constructive interference. Inexperienced surfers could get hurt. Have fun!