use Cat;

Here we have a module called Cat.pm

     #!/usr/sbin/perl
     package Cat;
     sub new {
        my $class = shift;
        my $self = {};
        bless $self;
        if (defined $_[0]) {
                $self->{'name'} = shift;
                }
        if (defined $_[0]) {
                $self->{'color'} = shift;
                }
        return $self;
        }

     sub meow {
        print "meow\n";
        }

     sub printDetails {
        my $self = shift;
        print "$self->{name}\n";
        print "$self->{color}\n";
        }
     1;

Let's use Cat.pm in a program called test.pl

     #!/usr/sbin/perl
     use Cat;
     my($cat) = new Cat("Fred", "white");
     $cat->meow();

There are an incredible number of modules out there for you to use at archives such as CPAN. In fact, the best way to go about practicing using modules is to go out and find some that you need. The fact is that there is probably a Perl module already written for all of the simple to complex tasks you will need for 98% of your projects. You needn't write the code yourself cause it has already been written!