Accuracy X/-X: A cumulative, static ability that means, "Add X to each of this unit’s attack dice." and "Subtract X from each of this unit’s attack dice." respectively. Accuracy can’t alter "natural" rolls to affect Critical Hit, Fury, or Parry, but it can affect your chance against Armor. If a unit gets the Accuracy ability after you roll attack dice, it's too late to affect the hits.
Armor
Armor: An isolated, static ability that means, "This unit can only be hit on a roll of 5 or more." Armor works against dice of damage and attack dice. It redefines what die roll is required to hit a unit. It doesn’t modify the die roll like Accuracy. A unit with Accuracy 1 attacking a unit with Armor hits with 4's, 5's, and 6's.
Pilot
[sub-type] Pilot: A layered, static ability written as "[sub-type] Pilot. The [sub-type] gets:… ." that means, "You may move this card onto or off of a non-Droid Space or Ground unit of the correct sub-type once during the build step. Ignore all other text on this card except its name, sub-type and health. The piloted unit can't have more than one Pilot." Treat all of a unit's Pilot abilities for a sub-type as a single Pilot ability for that sub-type. It grants abilities to that unit alone. See the "Pilots" section of the rules PDF for more info.
Shields
Shields X: A cumulative, static ability that means, "The attacking unit gets –X power against this unit." Shields only matters when attack dice are rolled. If you give a unit Shields after your opponent has rolled for damage, it doesn't affect the roll.