tcl means tool command language and tk is the graphical user interface for it and other languages.

There is shell that can be started in a console tclsh (or under Windows tclsh86.exe). The command exit brings you back. Alternatively you can write everything in a file

puts "Hello World"     

and tclsh hello.tcl or add the magic line pointing to the interpreter

#! /usr/bin/tclsh
puts "Hello World"

Set run permission on this file and run it as ./hello.tcl

Tk is not limited to just tcl it can also be used by other programming languages as python, where

import tkinter

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