#in the file Acme/Helloworld.pm
package Acme::HelloWorld;

use warnings;
use strict;

sub new {my $class = shift; bless {}, $class }
sub helloworld { print "Hello world!\n" }
1;

#in the file helloworld.pl

use Acme::HelloWorld;
my $h = Acme::HelloWorld->new();
$h->helloworld();