Clerics and certain Sorcerers can cast Heal. It has three versions
1 action: 1d8 per spell level to an adjacent creature. Heals allies and living creatures, but damages undead.
2 actions: Range is now 30 feet and if healing, heals an additional 8 per spell level.
3 actions: As the 1 action, but everyone within 30 feet.
Undead often fight among living creatures in this game, so try not to heal those, but the three action version is still impressive.