All attacks have specific damage ratings, indicating the number of dice that you roll for the attack's damage (called the damage dice pool). Some damage dice pools are based on the attacker's Strength, while others are based on the weapon used. Damage dice rolls are made versus difficulty 6. Each success on the damage roll inflicts one health level of damage on the target. However, the damage applied may be one of three types:
Bashing: Bashing damage comprises punches and other blunt trauma that are less likely to kill a victim (especially a vampire) instantly. All characters use their full Stamina ratings to resist bashing effects, and the damage heals fairly quickly. Bashing damage is applied to the Health boxes on your character sheet with a "/."
Lethal: Attacks meant to cause immediate and fatal injury to the target. Mortals may not use Stamina to resist lethal effects, and the damage takes quite a while to heal. Vampires may resist lethal damage with their Stamina. Like bashing damage, lethal damage is applied to the Health boxes on your vampire's character sheet with a "/."
Aggravated: Certain types of attacks are deadly even to the undead. Fire, sunlight, and the teeth and claws of vampires, werewolves and other supernatural beings are considered aggravated damage. Aggravated damage cannot be soaked except with Fortitude, and it takes quite a while to heal. Aggravated damage is applied to the Health boxes on your character sheet with an "X."
Damage dice pools can never be reduced to lower than one die; any attack that strikes its target has at least a small chance of inflicting damage, at least before a soak roll is made. Moreover, damage effect rolls cannot botch; a botched roll simply means the attack glances harmlessly off the target.
For more information see Health and Healing Times.