Perl CGI - Exercise

To get you thinking about CGI and how it works, examine a CGI application and describe how you think it might work.
There is no right or wrong answer here, the point is just to get you thinking about it.
Take a look at this CGI program and describe what you see and how you think it works. How would you go about creating a program like this?
Enter your answer in the area below, and click the Submit button when you are finished.