Trance is a physiological state of mind known to everybody. In daydreams, when you dream of your last holiday, you are in a trance.
Hypnosis is just establishing a planned state of trance. In the state of trance, working on goals, like planning success in your profession or sports is much easier.
In hypno-psychotherapy, fears, trauma and depression can be treated very effectively, with solutions often very creative and symbolic. Quitting smoking is also a common goal for hypnosis.