Answer 1

start from the basics, and after advanced, intermediate, ....
frontend: html, css, js + js framework, + bootstrap / tailwindcss
backend: php, mysql, mariadb, python, postrgesql, java, c#, ruby, and so on....

if you know what would you like to do, this is a really great guide, a roadmap....
https://roadmap.sh/

I hope this helps