Hi Rissy!
Healing is a skill just like any other in the game and it needs to be practiced. In the early stages it can be difficult to train a villager as a healer, but don’t give up!
Drag and drop a villager onto a sick villager until they start to learn how to heal other villagers. If you don’t teach your villager how to become a healer, they will not be of any help to your village.
You can also buy master healers in the game's Marketplace!