The combat example in the core book was a bit confusing, so what's the correct way defense works:

1)each point of defense from your armor add a misfortune die to attack that target you (seems to be what the example said)?

2) defense from armor add to your agility which the enemy compare his ws or bs skill to to add challenge die? (seems to make a lot more sense)

3) it works some other way?

#1 is correct

The default challenge rating of a melee or ranged attack is a single <P> challenge die. Each point of Defense add a misfortune die to the pool. Agility has no effect on Defense, except needing 3+ to get access to the Dodge basic active defense card.