How to become a professional Web or App developer?

Answer 1

https://www.upwork.com/blog/2014/03/10-best-web-development-tutorials-beginners/
http://bigemployee.com/how-to-build-your-first-web-application-tutorial-series/
https://www.tutorialspoint.com/android/index.htm

Answer 2

Learn:

For Web:

HTML
CSS
BOOTSTRAP
JS
PHP

For Android:

Java
Kotlin

practice more
and more

then seek for job openings
or you can work as a freelancer.