The main problem is that you have "use TK;" when you should have "use Tk;" (lowercase k). You should also have "use strict;". The "useless" warnings come from these lines:

	@tmplist;
	$key;

Update: You have a bug, by the way. You really should have my @tmplist; inside the sub xy, so it is initialized each time. Right now you keep adding on to a global array, but you keep using the same four coordinates from the beginning of the array. Since I'm feeling generous today--okay, I'm just avoiding my own work--here is the corrected program, with some stylistic improvements (IMHO):

use warnings;
use diagnostics;

use Tk;
use strict;

my @coLour = ('red', 'blue', 'green', 'black', 'orange', 'yellow');
my $width = 600;
my $height = 600;
my $randi = &randi();

my $mw=MainWindow->new;

my $canvas =$mw->Canvas(width => $width, height => $height)->pack(); 

for (1 .. $randi) {
  $canvas->create('line', &xy(), -fill => &randcolour())
}


MainLoop;

sub randcolour{
   return $coLour[rand(@coLour)];
}

sub xy{
    my @tmplist;
    foreach (1 .. 4) {
      push @tmplist, rand($width);
    }
    return @tmplist;
}


sub randi{
  return rand(50);
}
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