Hypnosis is a trance-like state in which people are more open to suggestibility, are relaxed and likely to process information differently. It is usually induced by gentle verbal repetition and mental images in a quiet and calm environment.

This phase is called ‘induction’ and the goal of the therapist is to focus the attention of the participant on the modulation and instructions issued by them.

Hypnosis is a state of extreme relaxation, intense concentration, and focused attention induced by a trained Hypnotherapist with a client to achieve a heightened state of awareness that is sometimes called a trance.

The person's attention is so focused while in this state that anything going on around the person is temporarily blocked out or ignored.
It is a natural altered state of mind that a person may be in and out of several times a day, whether on auto-pilot while driving, or zoning out listening to a Podcast or watching TV.

At the same time, it is a state of subconscious hyperacuity in which the conscious mind is bypassed and changes suggested. Hypnosis can be used to help you gain control over undesired behaviors or to help you cope better with anxiety or pain.

When a person is in Hypnosis, they are not unconscious and not under the control of the Hypnotist. 
It's important to know that although you're more open to suggestion during hypnosis, you don't lose control over your behavior. You are always in control.

During your Hypnosis session, your Hypnotherapist will make a series of suggestions that you have both agreed upon in a repetitive language pattern so that these suggestions will become embedded in the subconscious mind.

Over time the changes will occur naturally and organically as the subconscious mind takes the new direction and incorporates it into the changes that you want to see in your life.