Android wallet and payment integration

As cited by Wikipedia

A Payment Gateway is an e-commerce application service provider that allows credit card payments for e-businesses, online stores, bricks and clicks, or traditional bricks and mortars. This is the equivalent of a physical terminal for sale at most retail outlets.

In layman terms, you might have made purchases through Amazon or some other e-commerce site and used your debit / credit card to purchase stuff. The software that authorizes and completes the payment process is called a payment gateway.

Whereas a wallet is an encrypted storage medium used to store important financial data. The wallet may contain information about your cards. It can also contain digital money. (Digital money is money that you have already paid to the appropriate wallet authority, and you can use the money later, like Paypal does.)

Adding money to a wallet requires a payment gateway

For implementation and more information about them, you can refer to the Google Wallet integration in the Android app

To select a payment gateway, you can refer to http://business.tutsplus.com/articles/how-to-choose-an-ecommerce-payment-gateway--fsw-42468 .