As the leader and only healer of your guild, choose potential new recruits, upgrade your guild house and evolve your healing arsenal. Receive quests, visits from shopkeepers and get paid in exposure (EXP).
Pick your team mates and customize your line up before entering the dungeons! Remember they have a mind of their own and will battle by themselves and always blame the healer... But you can't do anything by yourself, so do whatever you can to keep them alive!
Check the job board and grab quests that will lead you into procedurally generated dungeons. Lead and support your party, they'll REALLY need it...
Choose your healing style: heal with holy power, mend with nature and elemental abilities, shield them from damage, be a plague doctor, or purify your team with happy little flames.
Upgrade your spells, customize and develop your healing abilities as you progress throughout the game.
Guild houses aren't cheap after all, so collect as much loot as you can when you dungeon dive ! Use that loot to pay rent, upgrade your guild house, buy new abilities, and pay recruits. If you don't meet your quota, you'll become a homeless healer, and you probably don't want that, right?