Hypnosis
is simply a relaxed state of focused attention. By temporarily bypassing your conscious mind, it gives you the power to make behavioural changes at a deep level than when you attempt to make changes at the conscious level.
One way to think about it is that hypnosis increases the communication between your conscious desires (like losing weight), and the unconscious mind (where your true power to change exists).
Hypnosis helps a person create the behaviours that lead to the goals they set for themselves.
Much of the time, your conscious mind is actually the bottleneck towards effecting true change, as its main role is getting you through the day in the here and now.
Making changes that can lead to your success requires changes to your beliefs about yourself, the world, and others. It also requires making real changes in your habits, preferences and behaviours.
It is more efficient to make these changes with as little interference from your conscious mind as possible. This way you can access the incredible processing power of your unconscious mind without conscious interference.