PressBooks is a content management system built on WordPress that allows users to input book content once and export it in multiple formats including EPUB, MOBI, PDF, and for the web. It utilizes HTML and CSS to style the content and has customized the WordPress admin interface and added features like custom post types, taxonomies, and metadata for book production. Exports are created using programs like KindleGen and Prince XML to generate files for iBooks, Kindle, and print-on-demand PDFs. During the presentation, the speaker demonstrates how to make a book on PressBooks in four easy steps and shares a sample book created with attendees.