Strahd, you'd add your armor rating to your Body attribute, adjusting it for augmentations or qualities that change your damage soak tests, subtract out any Armor Piercing modifications that the attack might have (not sure if ghouls have that on their claws, my guess is no), and roll the resulting number of dice. Successes on that roll cancel out damage points on a 1 to 1 basis. Any damage that is not negated is marked off your hit points.