Underground Hypnosis is a set of tutorials designed by hypnosisgallery.com. It has been specially designed to teach you everything there is to know about hypnosis:
How to perform hypnosis? In what context? What are the risks? Etc.. This is an interactive tool to teach you the tricks of the trade. You can choose between a free resource (such as the one you proposed) and a premium resource, you'll be immediately redirected to pages of information on how to use hypnosis on others and how to gain control a person by hypnotizing.