How does a multiple file upload work?

<?php 
  $numoffile = 5; //number of files to upload
  [i]//this is the directory you would like the files to go into 
  // Fix path of your file to be uploaded, don't forget to CHMOD 777 to this folder [/i]
  $file_dir  = "/var/www/uploaded";   
  if ($_POST) 
  { 
    [i]//if it is a post, loop through the $numoffile[/i]
    for ($i=0;$i<$numoffile;$i++) { 
      if (trim($_FILES['myfiles']['name'][$i])!="") { 
        [i]//creates the new file name with trimmed spaces[/i]
        $newfile = $file_dir.$_FILES['myfiles']['name'][$i];
        [i]//moves uploaded file from the tmp directory to the new directory with the file name[/i]
        move_uploaded_file($_FILES['myfiles']['tmp_name'][$i], $newfile); 
        $j++;
      } 
    } 
  } 
  if (isset($j)&&$j>0) 
  {
    echo ("Your file(s) has been uploaded.<br>");
  } 
    echo ("<form method='post' enctype='multipart/form-data'>"); 
  for($i=0;$i<$numoffile;$i++) { 
    echo ("<input type='file' name='myfiles[]' size='30'><br>"); 
  } 
  echo ("<input type='submit' name='action' value='Upload'>"); 
  echo ("</form>"); 
?>