Learn about how hypnosis works.
Hypnosis has several different forms, most famously it involves a trained hypnotherapist and a subject. But hypnosis can also be self taught and self practiced, this is known as self-hypnosis. Hypnosis is the technique by which you enter a subconscious trance like state. This does not mean you have no self control or free will, you can leave the trance at any moment you want. The idea of putting you into a trance like state is that you become more open to positive suggestions which embed in your subconscious.
Because of the way the brain works, multiple sessions either with a hypnotherapist or a hypnotic recording are required for the suggestions to imprint on the brain for longer. This reinforces the suggestion because of repetition and because it commits it to your memory. This makes avoiding calories for example much easier over repeated sessions. The subconscious and the conscious mind are interconnected, but you can’t really know the subconscious, it is unknowable, but it exerts influence over your conscious mind. It is also deeply powerful, by using the subconscious mind to your benefit, you find it easier to make positive changes. This is why hypnotherapists want you to ‘visit’ there.