Oreilly has a cool program called Open Books that lets you read some out of print books online.
See the book CGI Programming on the World Wide Web. Yes, this book is 15 years old. But it explains the basic tenets of the WWW in a simple manner.
You don't want to write production software based on the code in this book. After finishing it you'll want to start looking at libraries like CGI::Appication. But if you read this book first and understand it, you'll be able to quickly pick up what it is that tools like CGI::Application or Catalyst... or even apps like ASP.NET or Java Spring do, and be able to quickly realize the feasibility and/or limitations of different approaches to solve tasks.