Character health is measured using HP (aka Health Points or Hit Points). Constitution determines HP. HP = 2 x Constitution. (see Character Creation
During combat a character may take damage and temporarily lose HP. Other effects such as poison may also cause damage.
Current HP is tracked on the character sheet in a fractional form: n/X where X is total HP and n is current HP. To take damage, subtract the damage points from n.
If current HP drops to 0, the character is unconscious and loses their turns. They must rest or receive healing in order to recover HP.
Resting overnight recovers 1 HP. Resting for a full day, (taking no turns) recovers 2 HP.
Health spells and healing potions are very useful as they restore HP instantaneously.
In the Connaught campaign, the Abbot of Carney can provide healing.