Click on "Books" in the categories list on the left-hand side of the Amazon homepage.
Click on "Advanced Search" from the next menu on the left-hand side.
Type in any details you wish to search, such as author, subject, title or date, in the appropriate box on the form. Click the "Search" button.
Click on the book that interests you in the search results.
Select "Used" from just under the details. You'll see hyperlinks for something like: "38 new" and "8 used." The "used" ones are all second-hand books from private dealers.
Select the book you wish to purchase and click "Add to Cart." Base your choice on customer reviews of the dealer and the condition of the book, as well as price.
Repeat the procedure for as many books as you wish to purchase, then select "Proceed to Checkout" and fill in your details.