Many merchants offer their customers loyalty programs through which they can earn spending rewards, points, and other benefits. Your Wallet's Loyalty programs section lets you store a digital copy of all your loyalty cards.
You can find a list of featured programs in the Loyalty programs section. These merchants have integrated their systems with Google Wallet's so you can receive notifications from them, link your existing loyalty account, or sign up for a new one directly on the Wallet app.
If you have a loyalty account, but can't find the merchant on the list, you can add your membership ID manually by touching the + sign.