> Why? Please elaborate.

Tk's GUI object model is sitting at a reasonable maxima between trivial to make use of vs. triggering the events necessary to make the GUI active.

Small example. You want a button on your GUI that triggers a procedure called "process" when it is clicked, this is the code you need (if you are fine with the remaining defaults) (and assuming you used 'pack' as the geometry manager):

    button .process -text "Process Entries" -command process
    pack .process -side top