For each multiple of 11 points done per attack, the wound that is caused will drain the character of 1 hp. Thus, an attack causing 11-21 damage would cause the creature to bleed 1 hp per round, but an attack causing 22-32 damage would mean the wound bled 2 hp per round. A wound from 33-43 damage would bleed 3 hp per round and so on.
Creatures may also receive multiple wounds from separate attacks. If a creature was struck twice for 13 and 15 hit points in two separate attacks, each attack would cause a wound and altogether the character would bleed 2 hp per round.
Wounds may be closed by healing magic or by the cantrip, close wound. Eating a goodberry will close a wound (multiple wounds would require multiple goodberries). A healing salve poured into a wound will also close 1 wound per point of healing the salve does. A healing spell of any kind (cure light wounds, cure serious wounds, cure critical wounds or heal) or an aid spell of any kind will close all wounds that the body has sustained, as will a paladin's lay on hands. Finally, wounds may be physically bound with bandages. See Binding Wounds.
Various creatures exist that cannot be effectively 'wounded,' including jellies, manifestations such as demons, devils and undead (who, not being alive, cannot 'bleed'), gaseous creatures, golems and creatures composed of various materials other than flesh and creatures that naturally regenerate.
No effort is taken with determining what part of the body wounded, as for gaming purposes this would add little value.
Note that the damage caused by bleeding does not figure into calculations for stunning, nor does bleeding affect a spellcaster's ability to concentrate.
See Attacking in Combat