Here’s a good place to start: https://lispcookbook.github.io/cl-cookbook/gui.html#tk

Program below does not work with ccl.

load "~/quicklisp/setup.lisp")
(ql:quickload "ltk")
(in-package :ltk-user)
(declaim (optimize (speed 3) (safety 3)))
(defun main()
  (with-ltk ()
   (let ((b (make-instance 'button
                           :master nil
                           :text "Press Me"
                           :command (lambda ()
                                      (format t "Hello World!~&")))))
     (pack b))))
(main)

Correction. Program works correctly with sbcl & abcl & ccl.
I just needed to put a softlink to whish executable (tk)

Hi, I did little experiments here: https://github.com/vindarel/ltk-tests and this doc is great: https://peterlane.codeberg.page/ltk-examples/ (in addition to the Cookbook)