Like food? I assumed it added the amount of damage to the minimum and maximum of the weapon. Like, a sword does 20-25 damage, with food it does like 23-28.
Rings would take the percentage of that weapon and add to the weapon's base damage.
Again, that's an assumption. Ones like
@imnvs and
@FilthyGorilla are good with numbers and knowledgeable with the ins and outs of things like this, so I'd be interested in hearing from them or anyone else if I'm wrong.