First of all, don't try and master it all in 24 hours. Second of all, grab a book and just work on some of the examples. I know you may have this grand vision for the next MySpace or something but unfortunately you have to start with something smaller.
Here is the book that I have been using:
PHP and MySQL for Dynamic Web Sites: Visual QuickPro Guide
Larry Ullman
http://www.zend.com/images/publishers/big_19.gifIt's a little outdated, focusing on PHP4 but that in combination with great advice from this forum and other tutorials, I have slowly begun to understand PHP and the terminology/commands.
In a week I have created my own login system, learned own to secure it AND
most importantly I understand what every piece of code means that I have used so far. That doesn't mean I can code something from scratch without a reference but when I look at code I can finally say, "Yeah, I know what that means and how/why it's used."