From the introduction:
[The Turning Leaves] is a game to play by yourself about ongoing lives of a variety of adventurous characters, fast forwarding to every point in their lives in which their lives change, for good or ill. It is the interactions with one another which spur these changes.
The mechanics move forward. You watch what happens, decide why it matters to you, and add the details of the fiction. The characters live in a medieval fantasy world of your imagining. The game continues until you feel like you're done and then waits until you come back.