Preparation:
Configure your PHP installation so that it has the CURL extension installed and activated:
With Windows: Place this line in your php.ini file: extension=php_curl.dll
Linux/Mac: install the CURL extension sudo apt-get install php5-curl
Copy the file provided by PSWebServiceLibrary.php to the root of your Web server. We will explain how to use this library in this tutorial.
Note :
You can do this tutorial on a local drive even while your store is on the internet.

Create a file list_the_clients.php at the root of the web server that you have chosen.
Specify where to find the web server in your file:
require_once('./ PSWebServiceLibrary.php');
Configured this way, your file should be found in the same folder as PSWebServiceLibrary.php.