He noticed something in the water looked like a boat turned upside down, and it was. He was able to make oars and a mast and a sail for the boat, and set sail. While at sea, he encountered a ship which he discovered was an English vessel on her way back to London from Japan. And that is how he made his way back to England.
The story of Gulliver's Travels was published in 1726 by Jonathan Swift.