The Gutenberg project provides three sources of documentation:
Learn how to build blocks and extend the editor, best practices for designing block interfaces, and how to create themes that make the most of the new features Gutenberg provides.
Visit the Designer & Developer Handbook
Discover the new features Gutenberg offers, learn how your site will be affected by the new editor and how to keep using the old interface, and tips for creating beautiful posts and pages.
Help make Gutenberg better by contributing ideas, code, testing, and more.