If the goal is to get acquainted with Perl/Tk in particular, the method that put me well on my way very nicely (oh those many years ago) was to just play with and study the demo program called "widget" that is included in the Tk distro.
It really is a very nifty piece of work -- you can browse lots of different widgets (all the important ones, and a fair number of "special" ones), explore different kinds of options and controls, and use the tool itself to look at and even modify the source code while you're playing with it. Just run "widget" from your shell.
Also, look for and try out Tk apps that have been posted here at PM, for a broader sample of coding styles. (You may have noticed that our own zentara is a master of the Tk arts.) Coincidentally, one of my first posts at the monastery was a "fun with Tk" thing: Tk cryptogram (no, not cryptography) -- in fact it was my own "teach yourself Tk" app.