Whenever a character receives damage, that damage is divided by the total of his Toughness and any applicable Armour (round down) to determine the degree of Injury Penalty he suffers as a result. Half of the total Injury Penalty (round up) is taken as a Wound Penalty, with the remainder being Shock.
For example: a soldier is struck by an enemy wielding a sword. The attack inflicts 42 damage against the soldier's Toughness of 6 and Armour of 6. Since 42 divided by 12 equals 3.5, this translates into a -3 Injury Penalty, and more specifically as a -2 Wound Penalty and 1 point of Shock.