[polysemy]
"BOOK Tricks of the Java Programming Gurus" has a chapter that illustrates the concept well.
Also see "What is 'embedding'?" [L1 ].
RS: As a simple hint, you do embedding when your C code contains
#include <tcl.h> ... Tcl_Interp *interp = NULL; Tcl_CreateInterp(interp): ...
Then you can create new Tcl commands, link static variables from your C program to Tcl variables, but first of all have the power of Tcl at your fingertips ;-)