From the introduction:
The Story Engine is a deck of 180 cards for creating storytelling prompts for fiction, art, role-playing games, and more. You can use it on your own, or as a multiplayer activity.
The Story Engine has two rules:
1 - Don't put the deck away until you create something.
2 - Ignore any card, rule, or guideline that doesn't help you create.
A "how to use" guide for the various cards in the series.