Can you please tell me what these lines of code do?

$sub_category = 0;
            if (!empty($_POST['sub_category_id'])) {
                $is_found = $db->where('type',PT_Secure($_POST['category_id']))->where('lang_key',PT_Secure($_POST['sub_category_id']))->getValue(T_LANGS,'COUNT(*)');
                if ($is_found > 0) {
                    $sub_category = PT_Secure($_POST['sub_category_id']);
                }
            }

I look forward to any assistance