According to expert, hypnosis would mean to separate a subject from one state of mind to another, the another being non-usual conscious mind. Most of the time, it would appear as if the person who are being hypnotized are asleep. It would also mean to totally bring a person's mind to wherever intended by a hypnotist. True enough, a hypnotist is the one who gives instruction to the affected person in his/her unconscious state.
How does it actually work
A hypnotist at work would normally need a trigger which he will use to get the intended person into the hypnotized mode. This could be anything that can catch the person's focus including music, a hypnotism-induction object, or even as crazy as using verbatism. You might also be familiar with the famous "1, 2, 3, snaps fingers" method. That should be considered as a trigger too.
Who uses it
That is really the question, isn't it? Exactly who in this world would have the ability to talk people to sleep. Well, not many but surely there is Usually this type of people falls under the category of magician, or performers to be exact. These people, who, by their ability to make people fall under hypnotism are paid a handsome rewards, when people buy tickets to see their performances. Of course, this involves more than watching people sleeping on a stage. Let me give you an idea. Imagine a fully grown professional adult had forgotten how to spell. Yes, this actually happen in an act on a stage.
Why is it called magic again? Because it allows people to do things involuntarily, or at least that is what they thought. You see, when you want to hypnotize somebody, you would tell them to relax and calm their mind. People have minds of so many thoughts. With these hectic piece of mind, hypnotism cannot be conducted. Therefore, a relaxed mind have more susceptibility towards the trigger that will induce them getting into hypnotism. In fact, you can try it for yourself. Get a willing friend and tell him to really empty his mind. A successful attempt will allow you to give any instruction to your friend and see that he will follow. The funny part should come when you would think of any embarassing act that you want to see him doing. Just be sure, nothing dangerous.
Hypnosis can prove to be useful, if used properly. There are also some other uses of hypnosis that are known to these days. One of which would be the obvious relaxation technique. Some people might have too many problems clumped up in their heads that they need to be told to calm down. It helps. Hypnosis also proves useful in the medical field, where surgeons used hypnotism as a substitute for anesthesia.