my @array = qw(a b c d e f);
my @new_array = do_something(\@array); #<- note the "\"

sub do_something {
  my $array_ref = shift;
  my @new = ();
  foreach (@{$array_ref}) { #<- treat the ref as an array
    # do some stuff like build @new
  }
  return @new;
}