Once you have created your comic book you will need to format it using Amazon's guidelines and save it in a specified format such as pdf. Sign up for Kindle Direct Publishing and upload your comic. Create your listing and printing specification and then set your price. Make sure you research competition to help you create an effective description, cover and selling price. Submit your listing for approval and once reviewed and accepted it can appear on the Amazon and Kindle stores. Whilst Amazon will market your product if you have created a good listing, you will see more sales if you also market your work on social media, via your website or email list.