WordPress classes explained

https://developer.wordpress.org/reference/ is sometimes more useful or other links on that page like Getting Started with WordPress. But you’re better off with running Query Monitor to see what is happening on each page then looking up the concepts individually. I don’t think anyone learns WP in a day. I think they typically focus on a single topic at a time after referencing existing themes and plugins. GenerateWP can jumpstart you in a better direction as well by creating well-form code.

Part of the journey to learn is being able to see what is happening when you test new ideas. I highly recommend the tools below.

Good Stack Exchange Answers;

Interactive diagram for the template hierachy