Scientology is the belief (first put forward by L. Ron Hubbard) that some ancient alien race crashed (in ships that looked like DC-9s) and died on earth and their spirits are infecting our bodies, causing all the bad luck, negative emotions, and general doom and gloom in our daily lives.
The church of scientology will scan you with their plastic box (made out of a dial, a gauge, a buzzer, a light, and 4 or 5 wires) so they can tell you how many of these alien spirits are infecting you. Then once they have you believing you are infected, they charge you a modest fee (modest for some, outrageous for most) to pay for the task of scaring the **** out of you until you buy their entire line of BS hook, line, and sinker.
Then you continue to fork over as much money as you can, because until they get all of their money, there will be no treatment for you. The treatment consists of yelling at you and scanning you with other plastic boxes.
All in all, you can spend upwards of $100,000 per month on these treatments.
All the while, the leaders of the church take time out of their busy schedules of rolling around in cash to preach at their congregations that the average population is a bunch of idiots and needs the treatment too and that any and all criticism of scientology should be immediately met with the utmost hostility.
Of course I am reciting all of this from memory and my memory isn't the best. So I will let you watch this video, showing actual scientologists doing what they do:
http://www.youtube.com/watch?v=cuHF_br-DBs
Enjoy.