If you have completed filling out all of the tabs (General/Details/Shipping/URLs) after double clicking on the PP button of choice you are ready to sell. Nothing further is needed.
Let's start for the beginning. You will need a PayPal account.
In the BV web builder click on the button of choice (i.e. Buy Now)
A box with a PayPal button will appear on your page. Double click inside that box and fill out each tab.
On the URLs tab it asks you for the pages URL that customers will be sent to after completion of a sale or a page if they decide to cancel the transaction. You will need to make these pages and publish them to your public_html file. It's up to you what the pages say. Make sure there is a way to navigate back to your website from both pages.
this is my thank you page:
http://www.redhawk-archery.com/thank-you.php