The original FPC-TCL unit can be broken into several separate units.
An appropriate breakdown might be;
tcl_commands unit (to build and register a tcl command), tcl_channels unit (including file and socket channel types), tcl_events (...), tcl_hashtables, tcl_interpreters, tcl_namespaces, tcl_objects, tcl_strings, tcl_variables.
Thus, getting started with only the tcl_command unit is simpler.
I have not yet figured out why the FPC-TCL unit author did not use the ParamStr, and ParamCount functions. argc and argv are the glue between TCL commands. I don't understand the approach taken in the FPC unit.