According to W3Techs (which provides extensive and reliable web technology surveys), WordPress powers 40% of all the websites on the Internet.
Popular CMS by Market Share: https://websitesetup.org/popular-cms/
WordPress Website Showcase: https://wordpress.org/showcase/
SEO (Search Engine Optimisation) best practice: https://wordpress.com/support/seo/
Guides / Tutorials
Free Getting Started with WordPress eBook from iThemes Media. This handbook for beginners offers an introduction to WordPress, the open-source website platform. You’ll learn the benefits of using WordPress, as well as step-by-step instructions for getting familiar with the WordPress Dashboard. You’ll also learn about WordPress themes and plugins, how to create your first post or page, and optimize your site for search engine — all with helpful links to video tutorials.
How to Use the New WordPress Block Editor (Gutenberg Tutorial): Click Here to read a comprehensive tutorial on how to use the Gutenberg block editor in WordPress.