Well, I got my wisdom out of the O'Reilly book 'Learning Perl/Tk' (which is out of print, the successor is called 'Mastering Perl/Tk'). Especially if you want to do more with Perl/Tk it might be better to read about it yourself.

Luckily the chapter about pack is available online: http://oreilly.com/catalog/lperltk/chapter/ch02.html