When attacking, the character must roll (typically a twenty sided die plus or minus any modifiers) to ensure that they are accurate enough to hit their opponent.
vs. Armour Class[]
Physical attacks typically must beat the opponent's Armour Class, or the opponent successfully dodges.
vs. Magic Class[]
Magical attacks typically must beat the opponent's Magic Class, or the opponent successfully dodges or wills the magic attack to fail.
Called Shot[]
A called shot is more difficult, and requires a higher roll. For example, a Headshot adds a +4 to AC.