Generally speaking, if there were no influence on a body of water, be it a lake or the sea, the water should be still. However to quickly demonstrate how air in motion can influence a body of water using a scaled down model, one can simply take a cake pan and fill it with water.
By simply blowing on the surface, the force of the air moving across the surface will cause the water to ripple in the same direction of the air flow. If blown hard enough the ripples will move faster than the surface is capable of moving in the same direction, which in turn will cause the mini waves to break over just like you would see at the shoreline of the ocean or lake.
The oceans however are deep and massive. Wind generated waves are the most common, and because of the depth of the ocean any wind pushing the water surface will create much larger waves than the wind at the same speed would cause in a smaller body of water such as a lake.
There is another form of power that generate waves, and that is the gravitational pull of the moon, and also the rotation of the earth. The earth pulls the water towards itself until that part of the ocean is influenced by the pull of the moon.
If there were no wind at all, we would see the effects of gravity both from the earth itself and from the moon.
Another situation is under the sea quakes that can displace small volumes of water to cause larger than normal waves under normal conditions, as well as waves that would wipe out an entire coastline if the quake was larger. Generally, the height that an underwater quake pushes a portion of the sea bottom upwards, the wave generated will approximate the same height.
However when the wave reaches the shoreline, the volume of water racing to the shallow point will break over itself as it has no deeper water to continue on and will rise dramatically in height as it hits the shoreline.
Another example of what will cause gigantic waves are huge land portions that slip into a lake or from an island whereas the mass of land slipping into the water will displace unimaginable amounts of water in an instant and thereby causing what we know as tsunamis that can reach 1000' in height. These are rare, but always a threat.
