Make sure that you have an iPhone or Android phone with a data plan. (Currently, scanning is not available on iPads or iPod touches). While you are in a store you can easily and quickly earn rewards by tapping the "In-Store" tab at the bottom of the app. From here, you can check-in to your current location to see all the products available there for scanning. By clicking on a product, you open the barcode scanner, which allows you to scan the product.
For more information on how to scan products, please visit our blog post here: http://checkpointsapp.wordpress.com/2013/09/25/how-to-scan/