Go to the online retailer (Amazon.com, BarnesandNoble.com, etc.) and search for your book’s title, author name, and/or ISBN. Click your book in the search results to go to its product page.

Then, copy the URL shown at the top of the page. Anyone who clicks this link will be taken directly to your book on that retailer.

Note that it may take several days for your book to appear on retailers after publishing.