“DISCLAIMER: I read "Scientology: The Fundamentals of Thought" as part of a college course on religion and cults.
The "Church" of Scientology is a vicious and dangerous cult that masquerades as a religion. Its purpose is to make money. It practices a variety of mind-control techniques on people lured into its midst to gain control over their money and their lives. Its aim is to take from them every penny that they have and can ever borrow and to also enslave them to further its wicked ends.
It was started in the 1950s by a science fiction writer named L. Ron Hubbard in fulfillment to his declared aim to start a religion to make money. It is an offshoot to a method of psychotherapy he concocted from various sources which he named "Dianetics". Dianetics is a form of regression therapy. It was then further expanded to appear more like a religion in order to enjoy tax benefits. He called it "Scientology".
Scientology is a confused concoction of crackpot, dangerously applied psychotherapy, oversimplified, idiotic and inapplicable rules and ideas and science-fiction drivel that is presented to its members (at the "advanced" levels) as profound spiritual truth.
An illustrated synopsis can be found here: