How do the sea waves generate it's power that lashes the rocks and returns again to break it?

Most waves you see are generated thousands of miles from where you see them hit the shore. Ocean waves do not actually move water molecules around, but instead use a cyclic motion to transfer energy from one molecule to the next until it strikes land.

There are four controls on what kind of wave you'll get, and it has to do with the wind:

(1) Which way the wind is blowing

(2) How strong the wind is blowing

(3) The length of time that it blows the same way

(4) The area over which it blows (called the "fetch").

So you could have a typhoon off the Philippines that generates waves which eventually crash on shore at Mavericks (famous California surf spot...). Because the typhoon blew for three days straight (example only), the surfers could have great waves for three days... then it would go back to "normal" wave action. Yet even the normal action is created by winds; just not as dramatic.

Almost all waves are wind driven. The few exceptions are due to tides, earth quakes, land slides, and moving ships.

The "power" is mostly due to kinetic energy. If you want a good practical feel for the amount of energy involved. Get an empty 1 gal milk jug. Fill it with water. Hold it over your head and drop in on the floor. This gives you a sense for the amount of kinetic energy from a relatively small wave, sort of 6 feet tall. During hurricanes, waves on the ocean can be 100 feet tall.