We both roll a d100, one for offense (Attacker) one for defense (defender). We add up our various bonuses (from our stats or items in play) and whoever has the higher number at the end wins. In the event of a tie, the defender wins. If the defender wins, no damage is incurred and in the event of a poison attack, the poison is resisted. If the attacker wins, all stat changing effects take place (Poison, Hold, and so on) and damage is given according to Type, Attack bonus and any other applicable bonuses.