Essentially, our mind is split between the conscious and the subconscious. Hypnosis works with the subconscious mind, which controls 90% of our behavior. It is the storehouse of all of our emotions, memories, beliefs and patterns. The subconscious mind also controls our autonomic functions, such as breathing and our heartbeat. The conscious mind is that part of us that is logical, that can do arithmetic or solve problems.
Hypnotherapy is a technique that puts the patient into a relaxed state (through progressive muscle relaxation), which bypasses the conscious mind and contacts the subconscious. In this relaxed state, the subconscious can readily accept and act on new information and suggestions for healing, change, growth and attainment of individual goals. While in this state, you are still aware of yourself and are always in control. Relaxation and peace are usually felt throughout the process. It is like a "mental massage"!
In truth, hypnosis is something most of us have experienced in our everyday lives. If you've ever been totally engrossed in a book or movie and lost all track of time or didn't hear someone calling your name, you were experiencing a state similar to a hypnotic one. Or while driving home and thinking about other things (and not consciously paying attention to how to get there) but still making it home is another example of how your subconscious mind takes over because it has become a habit and pattern.