Coins are a valuable in-game currency used for several purposes: 

• Refilling lanterns during levels.
• Purchasing boosters to help with challenges.
• Speeding up lantern cooldowns in the Zen Garden.

There are several ways to earn Coins:

• Participate in special events.
• Complete in-game achievements.
• Connect your game to an account for the first time.

For larger amounts of Coins, the most direct way is to purchase them from the Panda Shop.