You’ll find a lot of good information in the WordPress Codex – Main Page ” WordPress Codex and WordPress › WordPress Developer Resources

To start with you’ll want to learn about the Template Hierarchy
and WordPress › The Loop.
Those are areas that are specific to WordPress that you’ll spend a lot of time with. WordPress › Theme Functions | Theme Developer Handbook | WordPress Developer Resources
is something you’ll want to dig into after you’ve got the basics. And there is a section on JavaScript Best Practices.
As you get more familiar with WP you’ll also develop a sense of when to use a plugin and when to code stuff yourself, be it a custom query or something you add to functions.php. (A wonderfully helpful file.)