What is William Paley's watch analogy and how does it attempt to explain creation?

William Paley gave his watch analogy in an attempt to prove that the universe has an intelligent designer. He asked us to imagine that we are walking through the desert and find a watch in the sand. A watch is a very complicated piece of equipment so we would assume that somebody had come to the desert before us and left the watch there, not that it had appeared there by chance. He also says that if we broke the watch into lots of little pieces and threw them into the air, we would not expect the watch to fall back down to the ground in on piece again. Paley says that we should apply the same logic when considering how earth was created. Something so intricate, complicated, and perfectly suited to its purpose could not have appeared by chance. It must have been put together by an intelligent creator, or 'watchmaker'.