Meaning: This sentence describes a situation where the ocean waves are crashing on the shore, causing sandcastles to collapse.
Choice of Words: Ocean is a large body of salt water. "Waves" are large bodies of water that move across the surface of the ocean. "Crashed" means that the waves hit the shore with great force. "Sandcastles" are structures built out of sand, usually by children. "Fell" means that the sandcastles collapsed.