[3.7] Action Rounds - An action round is a brief period of time - about two seconds - enough time for most characters to attempt a couple of actions. At the beginning of each round every character's used hit points become ready. Then the characters take turns trying to do various moves or combinations of moves until they all have no more ready hit points.
[3.8] Size Bonus - Larger targets are easier to hit, so the size of a target is added to the success roll of any attack against that target if the target does not defend. This also applies to inanimate objects. When a target tries to defend their size is already a factor because their attack, grapple, and dodge bonuses are effected by encumbrance (which is based on size). So size is not added to the success of the attack.