I would start by reading this post from -ninjex- viewtopic.php?f=79&t=9726
Now, you will need to learn some type of programing language. I like to use www.w3schools.com
they have a lot of online options to learn good and fast. However if you really want to learn, you should find a good ebook (or even buy a book from a book store) and try and learn that way.
As for hacking in general you need to look up how it is done. Learn what hacking truly is and how it works. You should look up some common exploits and vulnerabilities that people have found in the past, a site full of them would be https://www.owasp.org/index.php/Main_Page
It has a ton of hacking related pages.
As for a good site to learn hacking.... Well you are already there
Try to do the missions, get involved in the forum, you can even join the irc https://www.hackthissite.org/pages/irc/irc.php
. If you need any help with anything just hit me up and I will try and get you on the right course.