It's not a diet, it's a healthy eating plan. You can choose green days or original days. On either of those you have a list of "free" food that you can eat as much as you like of.
You then get 2 lists of "healthy extras", A's and B's. You have to have 2 A's and 1 or 2 B's (or might be the other way round). They are things like milk, cheese, fibre, to make sure you're getting the right nutrients.
Then anything else has a "syn" value. You can have between 10-15 syns per day.
It honestly works. I'm now a target member having lost 2st 3lb. I did mainly original days. A typical day for me would be:
Breakfast: Banana, cup of tea (I never eat breakfast - but you could have weetabix from healthy extra options).
Morning snacking: Things like grapes, apple, banana, strawberries (if hungry)
Lunch: Chicken tikka, cherry tomatoes, pepper, cous cous, raw carrot. Or jacket potato and cottage cheese.
Afternoon snack: Hi-Fi bar (A slimming world choc bar that's a healthy extra - they do one that is like eating a Terry's chocolate orange).
Evening Meal: Steak, tiger prawns, jacket potato, peas, coleslaw. Maybe Muller light for pud.
I'd still have butter on my spud and still have sugar in my drinks from my syn allowance, and there was scope for the odd biscuit at toddler group, or glass of wine.
On original days you can have a little bit of pasta with a huge pile of spag bol sauce, or a little bit of rice with a huge pile of chilli. On green days it would be as much rice or pasta as you want with a little bit of chilli or spag bol.
I didn't stick to it completely all the time. My philosophy was that if I went out I would have what I wanted and then get back with the plan the next day. It took me a year, but for me doing it that way meant I stuck with it. Going to group really helped too, I'd never have had the motivation to stick to it if I didn't go every week to get weighed and stay afterwards.
HTH