Attacks & Damage

Attack vs Armor Class

All attacks are made using a single standard 2d12 check, adding the damage dice of the weapon your using, along with either Dexterity or strength. Melee weapons will also add the melee skill to their roll, while ranged weapons will add the ranged skill.
This check is directly contested with the targets AC check, the result of which is subtracted from the damage roll.
If the damage roll is higher than the AC roll, it is considered a hit for the purpose of feats and abilities. If it is equal to or lower than the AC roll, it is considered a miss for the same purpose. Note that an attack hitting or missing ONLY accounts for AC, not for damage reduction or other ways to reduce damage taken. You could have damage reduction that reduces the damage taken from an attack to 0, but still proc on-hit abilities since it still got through your AC.

For example, lets say Jane is using a Rapier, has a dexterity of 3, and a melee skill of 2. She would roll 2d12+1d6+5 for the damage roll, and she ends up rolling a total of 21.
The person she's attacking has a 2 on dex, 1 point put into dodge, and an additional 5 AC from armor. They roll 2d12+6 on their AC check, rolling a total of 18. The AC total of 18 is removed from the attack total of 21, which means 3 points of damage goes through. This counts as a hit.

An AC check may also be called against AOE damage sources, such as those from bombs or spells, in which case the rules are similar (AC reducing damage).

Damage Types

There are a variety of different "types" of damage. This represents the many ways in which a creature can sustain injury, from cuts, to hammer strikes, to burns. There are 3 categories of damage, Physical Damage, Elemental Damage, and Mental Damage. Physical damage represents simple standard physical damage from everday things, falls, stabs, cuts, etc. Elemental damage is damage from more complex sources, such as fire, acid, or electricity. Finally, Mental damage represents damage to the mind, breaking a creatures will or shredding their sanity.
Physical damage is the most common kind, with elemental also being common but slightly rarer. Generally Mental Damage is the rarest, with very few abilities or monsters utilizing it.
While there are no specific mechanics for the roleplay effects of taking damage, it is generally advised to describe the effects of damage on your character as a battle goes on. For example, a character who has taken a lot of physical damage may walk slowly or with a limp, while characters who have taken a lot of Sanity damage may act more erratic or break down.

Physical Damage

Bludgeoning: Also refered to as Blunt for certain syntax, this represents blunt force trauma.
Piercing: This damage type consists of Stabs, pricks, and other pin-prick piercing wounds.
Slashing: This damage type is your cuts, slashes, and serrated wounds.
True Damage: The rarest damage, true damage is damage that cannot be reduced in any way.

Elemental Damage

Fire: Burns, fire, and other heat-based damage.
Ice: Frostbite, hypothermia, and other pieces of damage that occur from extreme cold.
Acid: The sloughing of flesh incurred by acidic chemicals or solutions.
Electric: Lightning, static electricity, and other shocking hits.
Necrotic: Anything that makes a human stop working from the inside out, e.g. snake venom.

Mental Damage

Will: Damage to ones mental fortitude and will to act.
Sanity: Damage to ones mental stability and general "mood".

Resistance & Vulnerability

Certain creatures, armors, abilities, and effects may invoke Resistance or Vulnerability. Resistance is synonymous to Damage Reduction, where you reduce damage by an amount equal to the number listed next to the resistance. This is typically aimed at a specific damage type, but it can be aimed at all damage types as well. The same goes for Vulnerability, except Vulnerability adds to the damage taken instead of subtracting.