I don't know if a working example would help, but here it is anyway:

#!/perl/bin/perl -w

use strict;
use CGI;

my $query = new CGI;

my @checks_list = qw(eenie meenie minie moe);
my @check_array = qw(eenie moe);
my %hash = (
    eenie  => 'Eenie',
    meenie => 'Meenie',
    minie  => 'Minie',
    moe    => 'Moe');

print $query->header(),
    $query->start_html(),
    $query->start_form(),

    $query->checkbox_group(
        -name    => 'group_name',
        -values  => \@checks_list,
        -default => \@check_array,
        -labels  => \%hash,
        -rows    => 2,
        -columns => 2),

    $query->end_form(),
    $query->end_html();
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