What is hypnosis therapy?

I have been wondering about lots of different kinds of techniques to get rid of things that bad habits, maybe even smoking, and I have heard that there are treatments that can work overnight. One of the things that I have heard really helps things is hypnosis therapy. Because it uses a part of your brain that is in your subconscience, there is a way to trigger things in that portion of your brain without all the thinking that usually goes into a decision, like to quit smoking. There are some addictions, but those can be broken easily with therapy.