So you wanna know how to hurt someone. Hurt them real bad. Well first thing you'll want is a weapon. Falling into at least one of the following categories, weapons deal different types and amounts of damage depending on their size, caliber (if a pistol) your stats, and proficiency in the skill required to use the weapon in question effectively.
Short Blades - Knives, stilettos and the like.
Long Blades - Swords, katanas, machetes and anything else thats long and edged
Pistols - Any caliber of handgun, which is single fire or semi-automatic
Rifles - Any firearm with a rifle stock that fires one shot at a time, including shotguns of any form
Sub-Machine guns - Powerful hand held firearms capable of a fully automatic setting.
Heavy weapons - Mounted high power or high rate of fire weapons
Melee - Hand held bludgeoning weapons like bats, chains, batons and any other random thing you might encounter
Your hands - Coupled with proficiency in martial arts or brawling your hands can be lethal weapons. There is a small number of weapons that add damage bonuses to brawling/martial arts attacks.
As for the conventional weapons named above, damage can be done to your enemy in a variety of ways. Opponents can be pushed off of roofs (Just as you can jump from them) to fall to the ground beneath, in some cases damaging them, in other killing them instantly. Damage can occur when exposed to the elements. Blistering heat and biting cold will have an adverse effect on your character, so take care in instances where you are at mother nature's mercy. New ways to be damaged or damage others are introduced as the code allows, things such as running people down with your vehicle are in the works.
In short, almost everything in Withmore can be wielded as a weapon, from a carton of fast food fries (although it doesn't make for a good weapon) to dildo (again, good to humiliate someone with, but not a fast way to end someone) to the myriad of weapons listed above. Last but not least the greatest weapon your character has is their mind. Be smart, be careful, be deceptive. Use your wits and you may not even need to wield a weapon against another.