How do archetypes help a story?
It helps the story because it helps the reader visualize the characters.
Archetypes are practically the same as stereotypes. They are people with typical characteristics e.g. 'the boss' is usually big and intimidating, booming voice, big stature, etc. This helps the reader visualize and connect with the character, making it easier to follow the plot. It also helps the character become more memorable, especially if the character plays a major role in the story.
Hope this helps :)