I assume you're referring to the table. The rows list attack types, the columns list armor types. So for every type of attack, this table shows how effective they are against a given armor. Higher values mean more effective (greater damage), lower values mean less effective (lesser damage).
So when you use a piercing weapon to attack someone with metal armor, this is much less effective than when you use the same weapon to attack someone who has just leather or organic armor. However, with an impact weapon it's the other way around, these work well against metal (and stone) armor.
