The official PHP web site as a lot of useful information:
    http://www.php.net/

in particular, the manual (bookmark this):
    http://www.php.net/manual/

One of the best things to do is just get PHP etc. installed and start
using it.  The best place to do that is with the instructions here:

    http://www.e-gineer.com/instructions

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Introductory PHP Tutorials:
---------------------------
(in no particular order)

Introduction to PHP :
   http://www.gimpster.com/php/tutorial.php
   - Basic, for the newbie.

Introduction to PHP :
   http://www.devshed.com/Server_Side/PHP/PHP101_1/
   - First of a Five part series on Devshed on the basics of PHP. 
     You really should check these out.

PHP Intro Review:
   http://www.builder.com/Programming/PHPIntro/
   - The folks at C|Net made a nice Intro to PHP

Vattekkat takes a stab at answering "What is PHP?"
   http://vsbabu.org/tutorials/php/
   - An overview on what PHP is. with samples.

PHP and MYSQL Basics (a bit MySQL oriented so ... )
   http://www.hotwired.com/webmonkey/databases/tutorials/tutorial4.html
   - Used to be the 'only' basic PHP article out there, still
     really good.  Deals a lot with PHP/MySQL together.

Using Strings with PHP
   http://www.zend.com/zend/tut/using-strings.php
   - This is VERY nice.  Print this out and read/reread.

PHPBuilder.com shares real-world uses with PHP
    http://www.phpbuilder.com/
    - If you're serious about PHP, bookmark this site.

PHPWizard.net Code examples and tutorials
    http://www.phpwizard.net
    - This site brought to you by the creators of phpMySql . . . great
things here!


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More Thoughts :
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The Key to learning PHP is just that, LEARN.  The manual is your
friend, this cannot be stressed enough.  Once you DO the tutorials
above (and during), going through the manual will help.  Don't try to
memorize it, that would be insane.  The manual is a reference on what's
possible with PHP.  Going through it you'll note many 'Functions' that
you'll later come to enjoy.  As you start coding your addressbook/links
manager ... the back of your brain will say "hmm, I _think_ I remember
something about stripping slashes?" so you'll head over to php.net , do
a search for "stripslashes" and you'll come across the stripslashes()
function (this is just an example). 

It's important (especially at first) that you read the ANNOTATED
manual.  Annotations are your friend.  Basically, people add useful
comments and tips on about every page in the manual so be sure to at
least scan through these.

   http://www.php.net/manual/ = annotated manual
   http://www.php.net/html/manual/ = non-annotated manual

Phew.  Still here?  As you go through the manual you'll find
interesting functions and 'things' that sound pretty cool.  Practice. 
Do.  Play.  Build.  Mess around with the examples, DON'T JUST READ THEM.

Lastly, it's useful to print out articles.  As you can lay in bed and
mark on them, ask yourself "What does this mean?" and later look it
up.  Oh yeah and if you're stuck, you can always post a question here :

   http://php.faqts.com/