On NETTUTS.com today there's a great tutorial that wants to teach you, the beginner, all about REST and how it works with the HTTP request and response methods to handle web service requests. A sample PHP application is also included to help you get a better feel for it.
The HyperText Transfer Protocol (HTTP) is the life of the Web. It’s used every time you transfer a document, or make an AJAX request. But HTTP is a relative unknown among web developers. This introduction will demonstrate how the set of design principles, known as REST, underpin HTTP, and allow you to embrace its fullest power by building interfaces which can be used from almost any device or operating system.
They talk about the reasons to choose REST for your application and look at some of the basics of HTTP, RESTful URL structure, the HTTP "verbs" and how to set up their example application. The application looks at the request method and shows how to handle the different "verb" request types. There's also a summary of the different HTTP status codes for responding to the client's requests (like 200 for success, 400 for a bad request, etc).