But first, a refresher on what CGI is and how it fits into the Web as a whole. As you know, the Web is the ultimate server-client application.
Clients are the programs on users' computers like Netscape and Lynx.
In the early days of the Web, people often tried to implement bits of it by hand, with varying success. A few got it right, many got it mostly right, and a few got it very wrong. CGI.pm gives you simple functions to put in your CGI program, and does it right. Because CGI programs are run in response to Web requests that could conceivably come from anyone on the Internet. They're a way for anyone to run a program on your Web server, so it's important to get everything right.