Nah its pretty simple. Essentially, you get to make extra attacks if youre using an agility-based weapon by subtracting 1 dice from each attack roll for each extra attack.
So if youre doing 2 attacks, you subtract 1 from each to-hit roll.
The cool thing is, other characters can do this too - but usually each attacks' damage is mitigated by the enemy's DR (Damage Resistance)
In your case, all of your attacks can combine against the enemy's DR once, making your strike much more potent.
Cheers
-LK