1: What is Changeling: the Lost?
CtL is all about fairytales. Specifically, fairytales with nightmarish twists. You've been stolen from the life you knew, forced into some form or other of captivity in the strange lands of the True Fae, and have been left forever changed by the experience.

2: What is a fetch?
Simply put, a fetch is a doppelganger of you that has been left behind by your abductor to hide your kidnapping. They are you in almost every way...the almost being that they aren't precisely you. They may be able to blend with mortals seamlessly, or there might be something off about the "new you". Either way, they convince the world that you're still around. Even if you escape from Arcadia, they remain in your place with your family. The worst part? They don't even know they aren't human. Then again, you aren't human anymore, either.