Personally I'd recommend reading the whole book first (Dukan is lifelong commitment so its probably as well to know what's ahead of you in every stage).
As to labels - you should be looking out for carbs AND fat, and aiming for as close to zero as you can with both. It's the percentage that counts.
Be very careful to check any product that has claims to be "low fat" or "virtually fat free" as many of these are loaded with added sugars and starches to make up with the taste and texture of the fat.
Perhaps it would be easier if you list some of the products you are thinking of buying, so we can give you more detailed advice.