My son for example takes 1 unit of fast
acting insulin (Novolog
in his case) for each 15 grams of carbs he consumes. Theoretically, when you are carb-counting such as my son, you can eat as many carbs as you want as long as you "cover" them with insulin.
One thing that was most helpful to us, especially at the beginning, was getting a Carb Counting book, one for fresh foods, packaged foods, etc. that you would purchase in the grocery store and then another one used for dining out.