Why did I get into learning PHP? Because I wanted to understand how a website was built correctly. I had a old website with blogging software from b2evolution, gallery from coppermine and couple of static pages put together not knowing how the code worked. So to upgrade things I started to learn how a website was built & developed, and what technologies were required.
The first part was to understand (X)HTML & CSS and then from that point you can go on to learn PHP with MySQL. You can find many tutorials online as an example of a resource of PHP tutorials at Nettuts. I also find buying an old book was very good as it meant that I was learning in a more structured manor then if I used online tutorials. So the book I brought was PHP 6 and MySQL 5 for Dynamic Web Sites: Visual QuickPro Guide and also PHP 5 Advanced: Visual QuickPro Guide (2nd Edition).
I have now finished the first book and will be finally starting work on my first PHP & Mysql application