It's not magic. It's a state of mind... a state of consciousness. Actually, even the professionals do not agree on a definition. As was stated by others, some people are more easily hypnotized than others. There are many factors involved but a skilled hypnoTHERAPIST works with the individual client to get through resistance that may be blocking him/ her from being able to enter into a desired state. If your question is: can everyone be hypnotized? Then the answer is 'yes, absolutely'.
What would you like to know about? If hypnosis is effective for what? There is a great deal of empirically based evidence for it's use on pain, somatoform disorder, and trauma. If there is a question about whether you can control someone else's will... the answer is no.... and playing with such an idea will bite you in the butt.