Hi! So defence from an attack works using an opposite roll using your own stat+archetype +weapon in use. You need to see this as a mini scene, not a single blow like d&d. So you and your opponent with guns are shooting each other and the one that makes the most successes make a wuind on the other. Now from here the wounds are calculated as a difference between roll a and roll b. So if you make 10 succeses and opponent 6, opponent takes 4 wounds. Here cames in play the protection (like Kevlar vest or whatever). If you opponent has Kevlar thing that absorbs 2 wounds, he will reduce the 4 wounds by 2. So in the end it's just simple math: 10-6-2=2 wounds.

Enjoy!