Learn php

That rather depends on what sort of programming languages you know already and what your experience level is.

Buy a book on the topic.
Read some online tutorials.
Or just sit down and start using it.

Lots of ways.

step #1 is having a good knowledge of html

I have found my way around with html and just starting messing around with files that came with the WP download. I still don’t understand much of it, but by trial and error and this wonderfull forum, I made most of the things that I wanted. I guess my way is just ‘learning by doing’.

thats the best way

When learning PHP be aware of which version is being offered. That goes for both online and printed material. The best thing to do is find out which version is loaded on your server and learn that version of PHP.