From the back of the book:
This free booklet gives you and five of your friends everything you need to play your first game of "Changeling: The Lost", White Wolf's all-new Storytelling Game of Beautiful Madness. Discover the wonder and terror of the Lost in "Dwelling in Darkness", a complete introductory scenario.
All the necessary rules are included. All you need is a few 10-sided dice and you're ready to go.
This book was initially released in print as White Wolf's giveaway for Free RPG Day 2007. It was later made available for free as a download.