Get yourself a cheap PHP book as a reference guide and then start reading the articles here on SitePoint!
PHP is a very easy language, in my opnion, although if you've never done programming before there is no shortcut. You need to learn the fundamentals and the structure. That means understanding what variables, data types, operators and functions are (nothing there is PHP specific). Structure is about understanding where and how you can use those things you just learnt.
If you're just interested in learning then you'll pick it up pretty soon, but don't think that will mean you can go and build some complex website. There's a difference between knowing PHP and being able to implement a secure site that has been optimsed for its end-purpose.