Scientology is a belief system created by American writer L. Ron Hubbard. It was based on 'Dianetics: the Modern Science of mental health', but was turned into a religion.
However, many countries do not recognise it as a religion, and there have been many court cases involving Scientology.
It's based on the idea that our behaviour is controlled by engrams (memories of past pain) and that once you learn to recognise them, you can make them disappear. The idea is to reach a state 'Clear' of engrams - from this lifetime, at least. However, this costs.
A person who has not reached a 'Clear' state is known as a 'Pre-Clear'. The Pre-Clear has to be 'audited' to reach a Clear state. This is done by a form of counselling called 'Auditing': the Pre-Clear sits opposite his/her Auditor, who asks questions designed to uncover engrams and help the Pre-Clear talks about them. Auditing is very expensive.
There are lots of websites about Scientology - mostly set-up by Scientologists, and some criticising them. Read both.