If you look at the tabs in the right-hand navigation area (Open, Contents, Recent, Tools, More), this page will usually default to Open. Switching to the Contents tab will give you a much more thorough sampling of the information available.
I don’t think you can treat any of this information as a comprehensive tutorial, but some of the Learning pages will help. And Grok Tiddlywiki helps cover that gap. When you’re looking to do more sophisticated things, some of the Reference topics should help.
I often find the main site tricky to navigate to solve particular problems I have, and I end up resorting to asking questions in this forum. It’s a friendly, helpful, and knowledgeable community; answers usually come quickly.
The trouble with using the main page as a learning resource is that teaching is just one of its main purposes. A year or so ago, the founder and chief maintainer of Tiddlywiki, Jeremy Ruston, described it like this:
This multi-focus does demonstrate the power of Tiddlywiki, demonstrating that you can use a single wiki for all that, but it can mean that the content you need is not always clearly in front of you. A number of people here (including me) have talked about ways to improve this documentation, but nothing very concrete has come out of it.