Basically you have a choice of 2 days: Red or Green. You have to decide what day you're on when you wake up in the morning and stick to it. It is easier to do seperate days to begin with, until you get used to what foods you can eat on what days and so on.
On a red day, it is mainly meat and a green day is unlimited amounts of rice, pasta, potatoes.
In the book you get, there are 12 pages of Free Foods. These are the foods that you can eat as much of as you like on that day. The more free foods you eat, the more you lose weight.
Then you've got Health Extras. You pick 2-3 of these every day. Things like brown bed, milk, cheese and so on.
Then there's syns (the best part!) You can have 15 syns a day but it is better to try and aim for 10 in the first few weeks until you get to learn the syn value of things. Syns are basically used for things like chocolate, ketchup, crisps, biscuits.
Some of it you have to measure, like your healthy extras, or you're only allowed a certain amount. But the free food, you can pick at all day long, providing you stick to you red day green day!