The golden coin icon at the middle of the upper part of your main screen displays how many coins you have. You can use them to purchase extra moves, lives, and powerful boosters that help you out in match-3 levels.
You get coins by completing levels and opening chests. Don’t worry about running out of coins—you can also purchase special coin deals at the coin shop: the Ipswich Bank! Access the shop by tapping on the coin icon.