Available resources for learning WordPress 4.7.2 from the ground up?

Question

My workplace is about to move to a swanky WordPress site from our ancient, never-upgraded ExpressionEngine site. I'm pretty good at hand-coding HTML for basic formatting, and I've watched about 6 hours' worth of "Creating a Wordpress site from scratch" videos on YouTube, including the specific themes and plug-ins we're getting (X, Integrity Stack, a few other bells and whistles).

Now that I have my feet wet, and more-or-less know my way around Cornerstone and the Inspector, I was hoping to find something like Codecademy or Scotch.io with actual hands-on training/experimentation, but so far I've come up short.

What tools and resources exist (if any) to allow a WordPress developer (especially a relative newb like me) to learn the functionality in a sandbox-like environment?

[Note: this is obviously similar to Resources for a complete beginner to learn to work professionally with Wordpress, but that was 6 years ago with no recent updates. If you'd prefer to close this question and update that one with updated data, I'd understand.]

Answer 1

I recommend the Theme Handbook of the official page, try creating a Theme using all of the features that are there, each one comes with example code, try copy pasting and adapting it to your theme.

The same with the Plugin Handbook try creating a plugin, reading the blog is good too, specially the development category, you can see how WordPress evolved and what new features and changes occurred.

Like in the post you mentioned the codex and the actual code are still a resource, i would add to it the developer search, which is great to search for function, classess, methods, hooks etc.