A story that tries to explain how something began or came about is called?

A story that tries to explain how something began or came about is called an origin story.

Here are some other terms that might be used depending on the specific context:

* Myth: A traditional story, often involving supernatural beings, that explains a natural phenomenon or a cultural belief.

* Legend: A story that is passed down through generations, often with some basis in historical fact but embellished with fantastical elements.

* Folklore: The traditional beliefs, customs, stories, and sayings of a community, passed down through generations.

* Creation myth: A story that explains the origin of the universe, the Earth, and humanity.

* Etiological tale: A story that explains the origin of a custom, a tradition, or a natural phenomenon.

The specific term used will depend on the specific story and its context.