Cart32 uses a set of standard set of HTML template files to generate the check out pages your customers see when they check out. Since these files are HTML, you can modify these templates to meet your specific needs by adding HTML, images, etc. You can access the template files by connecting via FTP to your ecommerce server or the Cart32 Hosting control panel this article.
The four standard checkout pages you see are (in order):
Other template files will be displayed based on your settings in the Cart32 administration. For instance, if you have your shipping settings configured to ask the customer for their zip code or country when they first add an item to the cart, this will use the template file called GetShipping.html. Other features use different template files.