Health is the final defensive layer in Last Epoch and If your health reaches 0, your character dies. Combine with other defensive mechanics such as resistances, armor, dodge, leech, ward and many others to make sure you health never reaches 0.
Health values can be increased through items, passives and by leveling up your character. Each character level grants +8 health.
Your character will also have some passive health regeneration, and it can be increased by skills, items, passives and leveling up your character. Each character level grants +0.125 health regeneration.