What you are looking to do is create callback functions. These are subroutines that are executed when the button is pressed.

For example:

    my $button1 = $mw->Button(-text => 'Quit', 
                             -command => \&exit);
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See how the function exit is the command that is executed when the button is pressed?

You may also supply other subroutines to be called:

    my $button2 = $mw->Button(-text => 'Quit', 
                           -command => \&my_sub);

    sub my_sub {
      print "Someone clicked me!\n";
    }
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There's a large number of Getting Started with Perl/Tk sites out there, and a number of books, too.

Hope this helped,
-v