How does Odysseus escape from calypso's isle?

He doesn't escape, he's let go. After Zeus says it's time to send Odysseus home, he describes what will happen on this last leg of the journey. Then, he send Hermes to tell Calypso it's time to send Odysseus away. She gives Odysseus some tools, they go into the forest and he builds himself a ship. She gives him some cloth, he makes sails. She supplies him and send him on his way.