Detox plans are all based on the same basic idea: cleansing and energising. You reduce the amount of energy you take in through food, cut out or at least limit toxins, eat a healthy, natural diet, drain your body by drinking lots of water and cleansing plant extracts, and exercising.
Detox plans are more or less scientifically proven to have a positive effect on the body, but they can vary quite drastically in length and in what you can eat (anything from nothing, fruit only, vegetables only, vegetable soup or stock only, no coffee, meat or sugar, etc.). Although you may well lose weight on detox plans, they are not weight loss plans.