In order to make purchases, you will need an active Google Play account for Android Devices or an active Apple ID account for iPhones. You will either need to redeem a gift card with monetary value to these accounts or connect them to a credit card. Once your account has been set up, simply tap the Buy button located at the top of your game screen. This will bring up a selection of chip packages currently available for purchase. Follow the instructions from there to make the purchase.

Setting up Payment for Google Play account

Setting up Payment for iTunes account