#!/usr/bin/perl -w
use Filesys::DiskFree;
$disc = '/dev/vx/dsk/var';

# get a handle object, you need to assign it to a var!
my $hadle = new Filesys::DiskFree;

# call a method on handle object but where do the ret vals go?
# if you want them you will need to put them into a var!
#$handle->avail($disc);
# assuming this method returns an array as you suggest
my @res = $handle->avail($disc);
use Data::Dumper;
print Dumper \@res;