If you are an amazon associate you just need to log into your account and click on the widgets tab at the top of the page. You can then select the type of widget that you want. The one on the website mentioned above is a carousel widget, but there are other types available too. You then pick the products you want to show, when done the widget code will be ready for you to copy and paste into your post or page and thats all there is to it.

Of course if you're not an amazon associate you would need to sign up first.