Windows

    A window is an area of  the  screen  which  is  currently being used.
    It usually has  the  background  saved  so  that  when  it is removed
    what was behind it is still there.

    A window has buttons  associated  with  it.   That is, buttons in one
    window are  not  necessarily  active  while  the  user  in playing in
    another window.

    I  strongly  recommend  you  trace   through  the  example  files  to
    understand how the system works.