Rupies are the lowest in-game currency. You primarily earn rupies by completing quests, from the Daily Bonus, from events, and by selling coop treasures.

Rupies are used in a variety of places, including but not limited to:

It is generally agreed that the best way to accumulate a lot of rupies is by joining coop rooms. Because it does not require any AP, players earn many treasures quickly that can be sold for rupies.