package MyModule;

# 'constructor'
sub new {
    # if you call MyModule->new, $_[0] will be 'MyModule'
    my $class = shift;

    # $self can be any reference, but usually a hash
    my $self = {};

    # this is the 'magic' that creates the object
    bless $self, $class;
    return $self;
}

sub half {
    # if you call $m->half(10), $_[0] will be the object
    my ( $self, $number ) = @_;

    # proceed as normal
    return $number / 2;
}

package main;
# now no longer in package, but in script

# instantiate object, call constructor
my $m = MyModule->new;

# yields '5'
print $m->half(10);