It is based on free food, you can eat as much of it as you like. Then you have healthy extras which are fibre and calcium based. Finally you have Syns which are your treats.
It sounds complicated until your SWC goes through it with you.
the free food, is either meat on a red day or
on a green day, carbs, such as pasta and potatoes
with certain things like fruit and veg being free on both days.