It pushes the first instance of each different item in @cn1_newnnn into the array @cn1_new and counts the number of repeats in %ss (assuming %ss is empty beforehand). Consider:

use strict;
use warnings;

my @cn1_new;
my @cn1_newnnn = qw(apple orange grape apple lemon banana apple grape)
+;
my %ss;

push(@cn1_new,grep {!$ss{$_}++} @cn1_newnnn);

print "$_: $ss{$_}\n" for sort keys %ss;
print "@cn1_new\n";
[download]

Prints:

apple: 3
banana: 1
grape: 2
lemon: 1
orange: 1
apple orange grape lemon banana
[download]