As Peterdjones said, a lot of it is metasuggestion. However, that is not the whole story, and there are ways to get the same effects without using the word "hypnosis".

On top of that, most of the interesting stuff just got buried under the label of "suggestion".

"Hypnosis" is a horribly vague word, but its basically all about learning how to talk to the different parts of the brain and engineering what you say as to get the different parts to respond the way you want. "Engineered placebo", perhaps.

What kind of answer are you looking for? I can't explain the whole lot in a short comment, but I'd consider writing a post on what researching hypnosis has taught me, if there's interest.