Hi Gemma
I only do the core plan online, so not sure what book it would be in.
Basically you have lists of foods that you can eat freely from, you can have unlimited portions of these foods, the only restriction being that they should be eaten only during 3 meals a day. Outside of meal times you can only have fruit or veg to snack on - anything else should count as points. You have 21 points a week to use, plus any activity points you earn.
The foods you are allowed are basically:
Lean meat
Fish & seafood
Eggs
Potatoes
Pasta, couscous, polenta etc
Beans, pulses & grains
Brown rice
skimmed milk
various cereals
ryvita
extra light soft cheese
all fruit and veg
low fat yoghurt, fromage frais etc
and all non-creamy soups
The focus is on eating until you are satisfied, rather than stuffed, which i guess helps to restrict your calorie intake beyond what you actually need.
Personally i find it gives lots of scope for eating normally with other people, or out in cafe's and restaurants as you only need to point what is extra to the core foods.