Basically a bunch of family and friends are worried about you, maybe you have a bad habit, or your life is on the wrong road, and they want to change you for the better. Its like a meeting of them telling you how they feel. If that's what you even meant by intervention.
An intervention class is a way to deal with addicted people about the disease and get them the help their needs. The class is planned to provide solutions to their problems, alternatives, expectations and covers everything one needs to know about it.