With the help of Athena guiding him, he cut Medusa's head off. In return, it woke the other two Gorgon sisters up in the process. Luckily, He had the cap of darkness on so they could not locate him.
Restoring the world
On Perseus's way home, he meets a maiden called Andromeda. It turned out she was to be a sacrifice. When he found out, he slayed the dragon as he slayed Medusa and asked for her hand in marriage. 
When Perseus made it home, he had learned her mother and Dicty's had to hide away. He had also learned about a banquet being held so he took his chances. He went to the banquet and when he saw polydectes, he took out Medusa's head, turning him to STONE.
Perseus was happy now, except, he never met his grandfather, Acrisius. When Acrisius heard, he tried to hide from him, in fear of the prophecy the Oracle had told him. While Perseus was searching for Acrisius, He came across a contest. On accident, Perseus hurled a disc that hit a bystander. That bystander was Acrisius.