1. Download and install XAMPP (free). You will need to run this software (or similar) to enable an Apache web server on your computer. In other words you need this to run PHP scripts.
2. Download and install Eclipse PDT All In Ones / Eclipse PHP Package (free). This is a development environment, a text editor and other tools, with which to create your PHP scripts.
3. Launch XAMPP. Start Apache, and MySQL.
4. Launch Eclipse. You will need to choose the “workspace”. The workspace is where you will save your php files. Generally you will want to use XAMPP’s htdocs folder. Found in the application folder where XAMPP resides. While XAMPP is running you will be able to launch your php scripts in a web browser by navigating to http://localhost/myScript.php
4. Find a book or tutorials. Start learning.