1.1. A Bit of History About Perl (and Tk)
Originally, Perl was written as a "quick-fix" to a problem Larry Wall was having with his job. Typical of all self-admittedly lazy people, he found a better and easier way to do it, and thus Perl was born. It has since evolved into a widespread and well-used language. Perl has been made available for numerous different platforms, has been well documented, and best of all, is license-fee free. Hopefully the reason you're looking at this book is because you're already converted to the way-of-Perl and want to know how to utilize it to the fullest.
The Tk extension to Perl handles all the widgets, whodads, and whatsits that combine to make a graphical interface. It was ported by Nick Ing-Simmons from Tcl/Tk for use with Perl. A common misconception is that you need Tcl/Tk installed in addition to Perl and Tk for the whole thing to work, but all you really need is Perl and its Tk extension. Thanks to a lot of work by a lot of other people, self-admittedly lazy people like me can download the binary for the machine they have and install it in less than 10 minutes (download time not included). You can also compile it from source for your machine.