What you get with tcl or any of the extensions is a mass of source code and some makefiles, sometimes with a configure script and sometimes without. Although there is a sort of vague standard for packaging tcl extensions, each author does things a bit differently. It helps to be familiar with makefiles.
The most standardized packaging is as you would expect, at the center of the language (Tcl, Tk, TclX). From there on out it can get trickier. Fortunately more and more authors are using gnu-configure to help you get a head start on the make.
I am not a talented C programmer, but I have managed (with help from the authors at times) to build all the Tcl code and tools I need. The only thing I really needed to improve was my ability to read and understand a makefile. Some of the make schemes for Tcl distributions are very complex. I have never yet met an author who was not friendly and (mostly) patient with newbie questions.
You will need quite a bit of disk space for your sources, especially when upgrade time rolls around and you have a couple of version of everything online at once. 20 MB or so would be a good start if you want to try out a lot of extensions. It could get larger.
Once you have a working wish and tcl, you can use or build most other applications written in Tcl easily. The first time you make Tcl/Tk you may do a lot of head scratching. By the third time it should be easy.