Don't worry about how it works! Just go to a group and have it all explained to you.
In a nutshell though, it works the same as all other diets, by restricting your intake of food in one way or another. WW restricts with points and SW restricts with Healthy Extras and syns (eg not too much bread, cereal, cheese and chocolate, crisps, alcohol) and emphasis on the free and superfree foods (protein, carbohydrates and veg/fruit).