Partner with Amazon and let them handle the transaction.
You have written, edited, and typeset your content. You have registered an ISBN and printed your book. Now, you must sell your book and ship it to your readers. If you are in North America and have worldwide distribution rights, consider applying for the Amazon Advantage program.
Upon approval, Amazon adds your title to its catalog and puts a few of your books in its warehouse. When customers purchase your book, Amazon processes and ships the orders. In exchange, you give Amazon a 55% discount from the suggested retail price that you set. Amazon also charges you a $29.95 annual membership fee.
So, if you gave your book a suggested retail price of $25, each sale through Amazon would pay 45%, or $11.25.
In addition to books, you can also sell CD music or VHS/DVD videos that you created, but not e-books. For more details on how to join the Amazon Advantage program, see http://www.amazon.com/exec/obidos/subst/partners/direct/advantage/home.html.