Your health, indicated by the on-screen health bar, is based on your current level and your engravings. Engravings can increase your health by a percentage when applied to armor (they also benefit damage and elemental perks). Your health is also increased by leveling up, wearing the correct armor for your level, and equipping certain weapons. You can find more info about engravings in our Reference chapter. Your health regenerates as soon as you are out of combat.