This is an interactive tutorial that walks you through how to use Wikipedia. It covers how to create an account, edit pages, message users, and navigate the site. It takes less than an hour to complete, and by the end you will be ready to contribute to Wikipedia.
Visual Editor
If you would like to try VisualEditor without editing a live article, here is a page where you can freely test it. You don't need an account to use VisualEditor on that page.
An introductory tutorial series is also available here.