Can someone please explain to me what the hell Scientology actually is?

I've searched for links and only come up with more questions. I know it's a US gov't recognized religion begun by L. Ron Hubbard (who proclaimed that starting one's own religion is a form of immortality), and that lots of celebs seem really keen to give them money, and that it spawned Battlefield Earth. But as for their actual beliefs? I'm getting nada, even on Scientology sites, other than non-Scientologists saying "What a crazy cult!"

So. What do Scientologists believe?

ETA:: Oh my lord. They are so scary. Thetans. I can't get over the body-snatching aliens. John Travolta, what the hell is wrong with you??