Hypnosis can be learnt quite easily. The best approach is through practice.
However, if you want to be proficient in it, then you got to take up a professional course and get certified. It is the same as learning anything. You could do self-learning and understand the concept, but to apply the theory, you need a coach or instructor to guide you through.
Especially for hypnosis, which is about altered consciousness, caution is still required when applying it.