List posts based on first letter of posts

This is the code I get from here, but I don’t remember the exact page, and this is my working page of letter B on my website (using the same code as you see below)

<?php
/*
Template Name: Locali per lettera

A WordPress template to list page titles by first letter.

You should modify the CSS to suit your theme and place it in its proper file.
Be sure to set the $posts_per_row and $posts_per_page variables.
*/

$posts_per_row = 3;
$posts_per_page = -1;
$pageURL = 'http';
$post_type="post";

if ($_SERVER["HTTPS"] == "on") {$pageURL .= "s";}
$pageURL .= "://";
if ($_SERVER["SERVER_PORT"] != "80") {
 $pageURL .= $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
} else {
 $pageURL .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];
}

$letters = $wpdb->get_col(
"SELECT DISTINCT LEFT(post_title,1) AS first_letter FROM $wpdb->posts
WHERE post_type="$post_type" AND post_status="publish"
ORDER BY first_letter ASC"
);

$first_letter = ($_GET['first_letter']) ? $_GET['first_letter'] : $letters[0];
?>

<?php get_header(); ?>

 <style type="text/css">
 .letter-group { width: 100%; border-top: 1px solid #444; }
  .navigation { text-align: center; padding:5px; margin: 0 10px;} 
 .letter { display:inline; color:#DDD;text-align: center; padding: 2px; border-top: 1px solid #48465B; border-left: 1px solid #48465B; background: #18181C; margin: 0 1px;} 
 .letter a{ color:#DDD;} 
 .letter-cell { width: 5%; color:red; font-weight:bold; height: 2em; text-align: center; padding-top: 8px; margin-bottom: 8px; border-top: 1px solid #48465B; background: #18181C; float: left; }
 .row-cells { width: 94%; float: right;  }
 .title-cell { width: 33%;  float: left; overflow: hidden; margin-bottom: 8px; }
.alignleft {
    float: left;
    margin-left: 25px;
}
.alignright {
    float: right;
    margin-right: 25px;
}
 .clear { clear: both; }
 div#a-z .padder {
    border-right: none;
    margin-right: none;
    padding: 20px 40px;
}
 </style>

<div id="main-background">

   <div id="main-column">
    <br />
      <h2><?php the_title(); ?></h2>

      <div class="margin-top"></div>

      <div id="a-z">

         <?php
         $mam_global_where = " AND LEFT(post_title,1) = '$first_letter' ";
         $paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
         $args = array (
            'posts_per_page' => $posts_per_page,
            'post_type' => $post_type,
            'orderby' => 'title',
            'order' => 'ASC',
            'paged' => $paged,
            'caller_get_posts' => 1
         );
         query_posts($args);
         $mam_global_where="";  // Turn off filter
         if ( have_posts() ) {
            $in_this_row = 0;
            while ( have_posts() ) {
               the_post();
               $first_letter = strtoupper(substr(apply_filters('the_title',$post->post_title),0,1));
               if ($first_letter != $curr_letter) {
                  if (++$post_count > 1) {
                     end_prev_letter();
                  }
                  start_new_letter($first_letter);
                  $curr_letter = $first_letter;
               }
               if (++$in_this_row > $posts_per_row) {
                  end_prev_row();
                  start_new_row();
                  ++$in_this_row;  // Account for this first post
               } ?>
               <div class="title-cell"><a href="https://wordpress.stackexchange.com/questions/105633/<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"> <?php the_title(); ?></a></div>
            <?php }
            end_prev_letter();
            ?>
            <div class="navigation">
            <?php
            foreach ($letters as $letter) {
               $url = add_query_arg('first_letter',$letter,$pageURL);
               echo "<div class="letter">";
               echo "<a href="$url" title="Starting letter $letter" > $letter </a>";
               echo "</div>";
            }
            ?>

            </div>
         <?php } else {
            echo "<h2>Sorry, no posts were found!</h2>";
         }
         ?>

      </div><!-- End id='a-z' -->
   </div><!-- End class="margin-top --> 
</div><!-- End id="rightcolumn' -->


<?php
function end_prev_letter() {
   end_prev_row();
   echo "</div><!-- End of letter-group -->\n";
   echo "<div class="clear"></div>\n";
}
function start_new_letter($letter) {
   echo "<div class="letter-group">\n";
   echo "\t<div class="letter-cell">$letter</div>\n";
   start_new_row($letter);
}
function end_prev_row() {
   echo "\t</div><!-- End row-cells -->\n";
}
function start_new_row() {
   global $in_this_row;
   $in_this_row = 0;
   echo "\t<div class="row-cells">\n";
}

?>