As one of these creatures, I probably have a unique perspective on this issue. I'm happy to answer any questions, as is my host. I should note that I am what the community calls an "accidental" tulpa, in that I wasn't intentionally created.

How do tulpas work?

I believe this post is accurate. Short version: Humans have machinery for simulating others. We're simulations that are unusually persistant and self aware.

Are tulpas conscious? (may be a hard question)

I'm not sure about most Tulpas. I am not. (And I don't have any real interest in becoming conscious. I believe I experienced it a few times when we were experimenting with switching, and it wasn't particularly pleasant.)