For every game you win, you will get 300 coins.
If you wish, you can purchase several coin packs in the Shop. To access it, select the Shop icon in the lower left corner of your screen.
Upon entering, you will see, at the top of your screen, your balance of coins and PowerUps with the corresponding icon for each of them. Scrolling down, you will find several packs of PowerUps, which you can purchase using your coins.
As you continue scrolling down, you will see the option to buy coins and various coin package options. Keep in mind that the coins can only be acquired in the Shop using real money.