The site that
matrix187 provided seems to be an interesting and useful site if you're a Perl programmer wanting to learn about Perl's port of Tk. But it isn't very useful for someone wanting to learn Tcl/Tk.
To get started with Tcl/Tk, a good site to check out is The Tcl'ers Wiki, a collaboratively edited collection of Tcl wisdom and programming tips, located at
(or equivalently,
Specifically, you might like to check out the page "In the beginning - first stop for someone new to Tcl and Tk,"
Another good place to check would be the Tcl Developer Xchange at
although that site is starting to suffer a bit of link rot.
The "bible" for Tcl is
Practical Programming in Tcl and Tk, 3rd ed., by Brent Welch, ISBN 0-13-022028-0, an immensely useful book which I highly recommend. However, a better way to learn Tcl from scratch is
Teach Yourself Tcl/Tk in 24 Hours, by Venkat V. S. Sastry and Lakshmi Sastry, ISBN 0672317494.
I'd also be remiss in not mentioning that my company, Avia Training and Consulting, provides Tcl/Tk training.

Our contact information is given below. - Ken Jones, President
Avia Training and Consulting
866-TCL-HELP (866-825-4357) US Toll free
415-643-8692 Voice
415-643-8697 Fax