It's one of the most base aspects of the internet and helps to connect users to the resources they're searching for, but it's surprising how many developers out there don't know how to work with it directly. WebReference.com is here to help with that in their new tutorial looking at the basics of the HTTP protocol.
The article is actually an excerpt from the Sams book "Teach Yourself Ajax in Ten Minutes", but it's one of the better overviews that I've seen. It introduces what HTTP is and some of the base components (request, response, formats, etc). There are brief code examples along the way to help with formats of things like the headers sent back and forth.
They move on to the status codes that can be returned and what each means. With the basic knowledge of a message format under your belt, they get into an example - working with GET and POST requests via a simple form (and what it's sending).