Star Wars - Hunters and Hunted
Cover is, quite simply, the easiest and best way to avoid getting shot available to characters. At its core, cover just means putting something solid enough to stop attacks between you and the attacker. It is applied in game as an abstract concept that revolves around how much vital area is exposed, rather than just an amount of concealed body area.
This image should help give an idea:
Frequently, assuming a lower posture (kneeling or prone) can improve the degree of cover, or even provide a bonus without something to actually hide behind. This does come at a cost in mobility however. Dropping to a kneeling or prone position can be done for free as part of a movement (including the free 2m step when making a full attack). Standing from these positions costs movement, 2m to stand from a kneeling state, and 4m from a prone state. Effectively, you cannot move as far in a round if you have to get up first (if making two move actions in a round, this penalty only applies to the move action in which the character stands).