On PHPMaster.com there's a new tutorial about working with cookies in PHP applications - an introductory look at what they are, how to set them and how to read their values.

Have you ever wondered that in spite of HTTP being a stateless protocol, when you log in to a website and buy stuff and checkout how the server can identify you uniquely? You might wonder if HTTP is stateless but your state is maintained through your interactions, isn’t this a contradiction? Welcome to world of cookies (not the ones which we can eat, btw :)), one the of primary ways to maintain user state and interaction between the web browser and the web server.

She shares a lifecycle of a common cookie and describes the parts of the setcookie method (parameters). There's also a few code examples showing how to read and write to them as well as update their values/expirations.