Nice and simple. You can take Stun Damage and you can take Wound Damage. Wound Damage total is higher than your Life Point pool you fall unconscious. If you decide to defend you roll your dice again . If your new total is higher than the attacker's then the attack is unsuccessful.
Damage is determined in the same way.
You and a taan both want to beat on each other with swords for awhile. The taan decides to take the attack, so he rolls his Agility Attribute and gets a 7. Because your total was higher than his, his attack is unsuccessful. Unfortunately, this doesn't help you much if its a PC vs. PC combat. Hopefully this oversight will be corrected in the full rules.