You basically make fresh lemonade and organic maple syrup, douse it with cayenne pepper and that's all you "eat." It's touted as cleansing your system of toxins but people use it primarily as a quick weight-loss method.
It's absolutely horrible for your body though. I mean, you're essentially "detoxifying" your body with pure sugar; a little lemon for diuretic properties to dehydrate you, and cayenne pepper to encourage some slight metabolic increase. Sugar is not a good way to detoxify a system that knows how to detoxify itself.
In other words, you're starving and dehydrating yourself while only eating sugar for energy. Doesn't detoxify and you lose a lot of water weight quickly and - of you can keep up with it - maybe weight.
If I recall correctly, you're also supposed to do a "Salt Water cleanse" where you drink water mixed with sea salt that acts like a laxative. That salt bombardment is so bad for the flora of your gut, you'll have indigestion problems for days afterward.