Hi there,
For Induction -which you may want to stay on for a few months until you have lost quite a bit of weight, is 20grams of NET carbs - that is the carb count minus the fibre count.
Once you are losing, and want to start adding foods (foods that are still on this eating plan though!), you can start adding things and checking to see if you are losing weight or if it is stalling you.
It's recommended to read the Atkins books, or at the very least their website which outlines foods, the number of carbs you are allowed to consume a day etc.
Hope this helps!