Coins are an in-game currency. They're used for several things:
🔹 Buying boosters;
🔹 Buying additional moves while playing levels;
🔹 Refilling lives;
🔹 Gaining other in-game benefits.
You can receive coins:
➡️ As a reward for beating match-3 levels;
➡️ As a reward for daily bonus;
➡️ As a reward for events and other in-game activities.