Basically, it works like this:
Say that you are going to try a disarm maneuver, and roll the appropriate skill (Fists or Weapons, usually)
Defender rolls to avoid the disarm
If the rolls are tied, then the maneuver puts a fragile aspect on the target, the target loses the weapon, and the attacker can get a free tag on the aspect. The target can probably use a supplemental action to pick up the weapon as soon as the fragile aspect disappears.
If the attacker has the higher roll, then either
1.) The number of shifts over the defense is the duration of the maneuver, and the defender won't have an opportunity to get back his weapon until the maneuver is over. Attacker gets a free tag on the maneuver
OR
2.) The aspect is sticky, and doesn't go away until either the end of the scene or the defender makes a skill roll to get his weapon back, opposed by the number of shifts the maneuver got. Attacker gets a free tag on the maneuver.