The Scientology home page says this:
The word Scientology literally means "the study of truth." It comes from the Latin word "scio" meaning "knowing in the fullest sense of the word" and the Greek word "logos" meaning "study of."(I emphasized that last bit.)
Scientology is the study and handling of the spirit in relationship to itself, others and all of life. The Scientology religion comprises a body of knowledge extending from certain fundamental truths. Prime among these:
Man is an immortal, spiritual being. His experience extends well beyond a single lifetime. His capabilities are unlimited, even if not presently realized — and those capabilities can be realized. He is able to not only solve his own problems, accomplish his goals and gain lasting happiness, but also achieve new, higher states of awareness and ability.
In Scientology no one is asked to accept anything as belief or on faith. That which is true for you is what you have observed to be true. An individual discovers for himself that Scientology works by personally applying its principles and observing or experiencing results.
I think that's a pretty good start. I'll continue with more tomorrow.