You must have at least some basic idea of HTML before you start this tutorial. You might want to take the HTML Tutorial first.
This tutorial on PHP is a complete tutorial for beginners.
This tutorial assumes that you know nothing about PHP. However a little knowledge about web terms like web server, browser, HTTP requests etc would be of extreme help. This tutorial tries to give you knowledge about almost all major PHP concepts like Variables, Operators, conditional calculation (If-Else etc.), form processing etc.
Wherever possible, the output of a PHP code example is given adjacent to the code itself. This will help you grasp PHP concepts easily.
If you have any doubt, just ask a question in PHP Forum.
What else, Just like all other tutorials on this website, this stuff too comes absolutely free!
Learn PHP For Beginners