Combat in SoIaF:
My Attack ist 12
Defense value of opponent ist 7
I hit with double succes (damage x 2)
damage - armor rating = damage done to the opponent
EDIT: Bevor you ask for each chapter and each rule in the new system you could take a look into the quick start rules, where things like this questions are explained in a fast and clear way.
Hope for the best, prepare for the worst