The Common Gateway Interface

You should first read this introduction to CGI to find out what it is, how it affects you, and where it came from.

Next, you should read the interface specification which will help you write a CGI script, or (if you are a server software author) add CGI compliance to your information server.

Finally, now that you're hopelessly confused, you should look at these examples to see what effect different requests have on the interface.