Slimming World is based on eating lots of food that are very filling, but low in energy. So you have free foods that can be eaten in any quantity, healthy extras portions that you can have so many of per day and then syns which are limited each day.
There is a list of super free food that is completely free on both days, things such as most fruit and most vegetables.
You can then choose which day you want to be on, either original (red) or green. On a green day you can eat unlimited pasta, rice, potatoes, beans, pulses etc plus 3 or 4 Healthy extras which are things like milk or cheese, cereal, bread or a small amount of meat or fish. On an original day you can have unlimited lean meat or fish as well as your 3 or 4 Healthy extras which in this case include a certain amount of potatoes in their skins or wholewheat pasta.
You can also have upto 15 'syns' everyday for things like treats (chocolate for me) or gravy and sauces. It stops you feelings deprived if you can still have treats.
Most people think its strange to be following a weight loss programme and to be able to eat as much as you want, but it does work but you do need to trust in the plan and follow it 100%. I found as you lose weight your appetite goes does naturally and you find that you eat less as time goes on.
If I were you I'd try to find a cheap starter pack on ebay and follow it. They now do another plan called extra easy but I only do red/green so can't explain that one very well.
I'll try to come back later to do an outline of WW.