You make a Disarm attack with a melee weapon against a target within that weapon’s reach, and then make a melee weapon Strike against them. If you Hit with your Disarm attack, you gain a +2 Bonus to your attack roll with the Strike in addition to the normal effects of the Disarm attempt. If you Critically Hit, this Bonus increases to +4.
If you Miss or Critically Miss with your Strike, you can make another Disarm attack against the target as a Free Action, with a +4 Bonus to your roll.
This ability does function, though only partially, against a target that is not wielding a weapon; if this is the case and you Hit or Critically Hit on the Disarm attempt, then they are not Disarmed but you still gain the Bonus to your attack roll.