Perseus's call to adventure was him needing a bride-to-be give for Danae and Polydectes. Polydectes talked about the Gorgons to Perseus, and Perseus decided to go to kill Medusa and bring back her head as the gift.
The Supreme Ordeal
The aid -the people who helped out Perseus- were Hermes and Athena. Hermes told Perseus that before he attacked Medusa he must be properly equipped with a sword to attack Medusa with which couldn't be bent or broken by the Gorgon's scales. Athena helped Perseus out by giving him a shield in which he'd look into like a mirror so he could avoid the Gorgon's deadly power.
Reward and the Journey Home
The test Perseus had to go through was getting the eye the Gray Women all shared so they would tell him the way to the nymphs of the North. Perseus successfully got the eye and they told him the way. He attained the equipment that he needed from the nymphs.
Restoring the World
The supreme ordeal is Perseus finding Medusa sleeping and he chops off her head. The other two Gorgons go to chase him but Perseus escapes.
The reward Perseus gets is Medusa's head and on the journey home he gets married to Princess Andromeda after rescuing her from a sea monster.
The way Perseus restores the world is by confronting Polydectes who has been trying to force Denae to marry him and killing Polydectes by using Medusa's head to turn him to stone. Polydectes' brother, Dictys, becomes the new king of the island.