This stuff can get complicated. I recently read beginner books on HTML, JavaScript, PHP&MYSQL, and finally AJAX. I read the Head First books as I found they brought it to my level of experience (basically no experience). Now I am at least able to surf around and put snippets of code together.
HTML is full of objects that can be manipulated on the fly with Javascript (client side programming) PHP is your server side language that can interact with MySQL
AJAX is a good bridge between the two, but you can always just use PHP to do the same thing.
I would study PHP & MYSQL first and then branch out.