Obtaining Tcl/Tk
Look at places to find Tcl binaries and sources or the ones listed here for your convenience:
Binary distributions for common platforms
Source code
Extras you should have
How to make Tcl/Tk work on my computer
Learning Tcl/Tk
Once you've got Tcl/Tk on your computer there are a number of pages that will help you learn about Tcl and Tk
Getting deeper
There are also a number of books available
Also available is the Tcl Tutor program and various Online Tcl and Tk Tutorials.
Web resources worth visiting include
Advanced resources