求教两段代码！

关于网页后台加密的代码，找到一段代码但因为我是初学所以看不太懂！
请高手能给解释一下最好能逐行注解一下，谢谢了。[因为这段代码是通过DW点拖的方法实现的可能有部分是垃圾代码]我在这个地方已经卡了一周的时间了，还请大家多帮忙，谢谢了！:)
<?php
// *** Validate request to login to this site.
if (!isset($_SESSION)) { //设定session
  session_start();
}

$loginFormAction = $_SERVER['PHP_SELF'];
if (isset($_GET['accesscheck'])) {
  $_SESSION['PrevUrl'] = $_GET['accesscheck'];
}

if (isset($_POST['yhm'])) {
  $loginUsername=$_POST['yhm']; //yhm 用户名
  $password=$_POST['mima']; //mima 密码
  $MM_fldUserAuthorization = "";
  $MM_redirectLoginSuccess = "1.php"; //如果登陆成功则进入此页
  $MM_redirectLoginFailed = "index.php"; //如果失败则进入此页
  $MM_redirecttoReferrer = false;
  mysql_select_db($database_conn, $conn); //连接数据库
  
  $LoginRS__query=sprintf("SELECT usid, uspw FROM user WHERE usid='%s' AND uspw='%s'",
  get_magic_quotes_gpc() ? $loginUsername : addslashes($loginUsername),             get_magic_quotes_gpc() ? $password : addslashes($password));
   
  $LoginRS = mysql_query($LoginRS__query, $conn) or die(mysql_error());
  $loginFoundUser = mysql_num_rows($LoginRS);
  if ($loginFoundUser) {
     $loginStrGroup = "";
   
    //declare two session variables and assign them
    $_SESSION['MM_Username'] = $loginUsername;
    $_SESSION['MM_UserGroup'] = $loginStrGroup;             

    if (isset($_SESSION['PrevUrl']) && false) {
      $MM_redirectLoginSuccess = $_SESSION['PrevUrl'];       
    }
    header("Location: " . $MM_redirectLoginSuccess );
  }
  else {
    header("Location: ". $MM_redirectLoginFailed );
  }
}
?>
<form name="form1" method="POST" action="<?php echo $loginFormAction; ?>">
  <label>用户名
  <input name="yhm" type="text" id="yhm">
  </label>
  <label>密码
  <input name="mima" type="password" id="mima">
  </label>
  <label>
  <input type="submit" name="Submit" value="提交">
  </label>
</form>
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<?php
//已经加密的页面
if (!isset($_SESSION)) { //看session是否已经存在
  session_start();
}
$MM_authorizedUsers = "";
$MM_donotCheckaccess = "true";

// *** Restrict Access To Page: Grant or deny access to this page
function isAuthorized($strUsers, $strGroups, $UserName, $UserGroup) {
  // For security, start by assuming the visitor is NOT authorized.
  $isValid = False;

  // When a visitor has logged into this site, the Session variable MM_Username set equal to their username.
  // Therefore, we know that a user is NOT logged in if that Session variable is blank.
  if (!empty($UserName)) {
    // Besides being logged in, you may restrict access to only certain users based on an ID established when they login.
    // Parse the strings into arrays.
    $arrUsers = Explode(",", $strUsers);
    $arrGroups = Explode(",", $strGroups);
    if (in_array($UserName, $arrUsers)) {
      $isValid = true;
    }
    // Or, you may restrict access to only certain users based on their username.
    if (in_array($UserGroup, $arrGroups)) {
      $isValid = true;
    }
    if (($strUsers == "") && true) {
      $isValid = true;
    }
  }
  return $isValid;
}

$MM_restrictGoTo = "index.php";
if (!((isset($_SESSION['MM_Username'])) && (isAuthorized("",$MM_authorizedUsers, $_SESSION['MM_Username'], $_SESSION['MM_UserGroup'])))) {   
  $MM_qsChar = "?";
  $MM_referrer = $_SERVER['PHP_SELF'];
  if (strpos($MM_restrictGoTo, "?")) $MM_qsChar = "&";
  if (isset($QUERY_STRING) && strlen($QUERY_STRING) > 0)
  $MM_referrer .= "?" . $QUERY_STRING;
  $MM_restrictGoTo = $MM_restrictGoTo. $MM_qsChar . "accesscheck=" . urlencode($MM_referrer);
  header("Location: ". $MM_restrictGoTo);
  exit;
}
?>
此页为受保护的页，未登陆不应看到

在第一段的代码的头部还有个引用外部文件我忘加了，里面设置的就是与数据库的连接


<?
//登陆页面
require_once('../Connections/conn.php');
?>

怎么没人理我？
:'( :'( :'(

一看就知道是dw生成的代码.
如果你想学php,建议你不要用dw的功能生成代码.
代码要自己写,不会可以先学基础.要不很难会有进步.
我以前也是那样,用dw.基础没有想好就想做一些论坛之类的
走了很多弯路...

我现在是在学代码的。可就在这个加密的地方卡住了。所以我想通过这个代码来了解怎么做，这段代码是别人给我的。
我就想知道怎么能实现上面的功能[具体的办法]。
给大家添麻烦了，谢谢。
急盼指教！！！！！！！！！！！！

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太感谢了！麻烦前辈了！谢谢！
仔细研究中···················