If it's a comma separated list, use split.
my @members = split /\,/, $hash{$key};

If it's a hash of arrays, use foreach.
foreach my $member (@{$hash{$key}})

If it's a hash of hashes, just pull out the data.
foreach my $member (keys $hash{$key})

For more details, show some code and explain what isn't working as expected.