How to learn how to pull WordPress sites?

Question

CMS

Hello everyone, I decided to learn WP at the level of stretching sites on CMS. The next question is what should I learn in PHP and is there any sensible material on WP itself without water?

Answer 1

https://codex.wordpress.org/

Answer 2

Russian version -
wp-kama.ru (off site) - https://codex.wordpress.org/
For a quick site, small notes (once written for one of the users):
https://yadi.sk/d/5ARTiBzq3QX5Wu