You should first read this introduction to CGI to find out what it is, how it affects you, what you can use it for, and where it came from. It's not as painful as you might think. Once you have a basic idea of what CGI is and what you can use it for, you should read this primer which will help you get started writing your own gateways. If you are interested in handling the output of HTML forms with your CGI program, you will want to read this guide to handling forms with CGI programs .
Security is a crucial issue when writing CGI programs.
Please read these tips on how to write CGI programs which do not allow malicious users to abuse them. When you get more advanced, you should read the interface specification which will help you utilize CGI to the fullest extent. If you are a server software author, it will help you add CGI compliance to your information server. Examples of CGI behavior and programs You may wish to look at this page of examples which demonstrate how the client URL affects the interface variables. We have created an archive of CGI programs on our FTP server.