Perseus was invited to Polydectes' party on how he was getting married. Everyone who attended brought gifts but for Perseus. Earlier Polydectes had talked to perseus about how the greatest gift of all would be the head of a fearson monster called Gorgons.
How he meets Hermes and Athena is not told, but Hermes offers Perseus a sword that cannot be bent or broken. On the other hand, Athena offers Perseus a shield that can be used as a mirror to be stealth and take down Medusa.
Reward and the journey home
Perseus steals the eye of Graeae's single eye to tell him the location of Medusa's lair.
Restoring the world
By using the gifts Perseus received from Hermes and Athena, he takes out Medusa by slicing her head off.
Perseus' reward was Medusa's head. However, on the way back home, he met this beautiful girl named Andromeda. She was chained up to a point where she was almost eaten by a sea monster. The reason why she was chained up was because of her beautiful mother boasting on how beautiful she was to some extent. That being said, Perseus rescues her and takes her home with him to be his wife.
There was really no restoring the world, but when Perseus pulls out Medusa's head, Polydect turns into stone. Adding on to that, Perseus marries Andromeda