The Hero's Journey is a framework that scholar Joseph Campbell came up with that many myths and stories follow. Many storytellers and story-readers find it a useful way to look at tale. (That's actually putting it lightly. Some people are straight-up obsessed.) Chris Vogler adapted Campbell's 17 stages of a hero's journey, which many screenwriters use while making movies. Vogler condensed Campbell's 17 stages down to 12, which is what we're using. Check out a general explanation of the 12 stages.
Tests, Allies, Enemies
Jason and the Argonauts face and defeat all kinds of enemies on the way to fetch the Golden Fleece. Harpies, giants, a king who's a little too into boxing—all fall before the mighty Argonauts. Our heroes also make a lot of friends along the way too. There's King Phineus, the ladies of Lemnos (who are super friendly), and also the sons of Phrixus, the guy who originally brought the Golden Fleece to Colchis.
Approach to the Innermost Cave
Jason and the Argonauts finally near Colchis, the land of the Golden Fleece. Jason has just gotten the surprise news that there's a dragon guarding the Fleece, so he's more than a little freaked out.
King Aeëtes says he'll give Jason the Golden Fleece as long as he completes three tasks: till a field with some fire-breathing oxen, defeat some warriors grown from dragon teeth, and defeat the actual dragon that guards the Golden Fleece. With the help of magical Medea, Jason passes these stupefying tests with flying colors.
Reward (Seizing the Sword)
Jason grabs the Golden Fleece and the Princess Medea, hops back into the boat with his buddies and makes his getaway across the sea.
The Road Back
As Jason, Medea, and the Argonauts sail back to Greece, they are chased by King Aeëtes. Medea decides to distract her father by chopping up her brother and throwing his body parts overboard. This grisly tactic is effective and the... um... heroes make their get-away.
Jason and Medea have a symbolic resurrection when they are cleansed of the murder of Medea's brother by the sorceress, Circe.
Return with the Elixir
Jason returns triumphantly with the Golden Fleece, but will his dreams of the throne of Iolcus come true?