Well to Juice cleanse or juice fast as it is more commonly known, is for people who want to loose weight but get all the minerals, nutrients and vitamins the body needs in a drink without having to eat. If your not new to juice fasting, but just need some recipes, check this site for some juice cleanse recipes.
When people do this they will generally fast for 1 day, 3 days, 5 days or 7 days. It is possible to loose a lot of weight by doing this, but i must stress that you have to follow the recipe guidelines properly. Starving your body can be very dangerous, so it is important that your body still gets the much needed minerals, nutrients and vitamins.
The most difficult part many face after juice cleansing is keeping the weight off. When you loose weight so quickly it is very easy to go back to old habits. So for a newbie i would suggest doing a one day fast once a week and build it up. Then create new lifestyle habits, so that when you reach your desired weight you can find it easier to stick to your new habits.