The post discusses extending Netlify CMS by creating custom widgets. The example project uses reveal-md to create web-based slideshows from Markdown documents. To start, you need to get a build system set up that allows you to use ES6, npm modules, and JSX. Then, install netlify-cms as a dependency, create a cms.js file, and register the new widget with Netlify CMS. The minimum viable widget is created using React, styled-components, and the CMS's built-in widgets. The post explains how to add controls for creating, deleting, and moving slides, including using props passed in by the CMS. By following this guide, you should now be able to create your own custom widgets to extend Netlify CMS to fit your content.