Yet another fine tutorial has been posted over on PHPit.net today, this time dealing with the use of the cURL library in PHP.
Sooner or later you're bound to run across a certain problem in your script: how to retrieve content from other websites. There are several methods for this, and the simplest one is probably to use the fopen() function (if it's enabled), but there aren't really a lot of options you can set when using the fopen function. What if you're building a web spider, and want to have a custom user agent? That isn't really possible with fopen, nor is it possible to define the request method (GET or POST).
That's where the CURL library comes in. This library, usually included with PHP, allows you to retrieve other pages, and also makes it possible to define dozens of different options.
This article doesn't look to be comprehensive on the topic, but does provide a great introduction to the hows and whys of using cURL in PHP. There's no installation procedures here, so you'll need to already have it installed, but other than that, you should have a great grasp on things by the time you're through.