At some point, you will come across a type of mob that will attack and injure your pet. Unless you want your pet to die, you need to heal it. To heal your pet, you will need to feed it herbs. The herbs are acquired from farming or you can purchase them from other players. The amount of health restored to your pet depends on the quality of herb you feed it. You can feed herbs to your pet by double clicking the herb icon in your inventory, or you can drag the herb icon to a free quick slot.