The answer to this question can be tricky, depending on your skill level with HTML and websites in general. If you are already editing HTML files manually, you'll find it easy to copy the button code into your site via your normal method of editing.
However, if you use a CMS or blogging platform like Wordpress, Joomla!, Drupal, or Blogger, you'll need to edit your post or page, select or view the HTML source and paste the button code there.
Alternatively, you can look at your button code and extract the URL (normally http://bitbuffet.com/buy/x/x/) and simply create a link on any text or image you desire.