The catalog page is layed out as an example of how you can set up your product sales page. This page does not use an ecommerce shopping cart solution although there are many ecommerce solutions available. This catalog page is a simple table based layout that includes the PayPal 'Add to Cart' button. The PayPal button is created on the PayPal website, then inserted into the product page. If you wish to use PayPal buttons you would need to sign up for a PayPal account. You can then edit the properties of the included PayPal buttons, or use a PayPal button wizard tool to insert the buttons for you.
The 'View Large Image' link opens a lightbox window which displays a larger product image and description.