Hi you can google intermittent fasting for a more detail description.
but it is basically in a nut shell where you fast without consuming any calories for 16 hours.
and then you have a window of 8 hours in which to eat.
then once a week you will have a fasting period of 24 hours.
The aim is to give your digestive system a breather because we have all been programmed to eat continually, but it truly isn't necessary because humans where designed to go extended periods of time without eating and when we put on weight that is essentially our bodies storage method when it has had more than it necessarily needs. the trick of IF is it trains your body to use the fat supply that it has stored on hand to function instead of continually using fresh accessible calories that are constantly supplied to it.