พอดีจะทำ login เป็น md5 ทำแร้วไม่ค่อยเข้าใจอะครับ ช่วยอธิบายให้ฟังหน่อยนะครับ

<?php
  session_start();
  include('connect.php');
  $passmd5=md5($_POST['password']);
  $strSQL = "SELECT * FROM member WHERE username = '".mysqli_real_escape_string($con,$_POST['username'])."' 
  and Password = '".mysqli_real_escape_string($con,$_POST['passmd5'])."'";
  $objQuery = mysqli_query($con,$strSQL);
  $objResult = mysqli_fetch_array($objQuery,MYSQLI_ASSOC);
  if(!$objResult)
  {
      echo "<script>
      $.alert({
       title: 'username and password are invalid.',
         content: '',
           buttons: {
             OK: 
      function(){
          window.location.href = 'index.php';
         }
          }
          });
        </script>";
  }
  else
  {
      $_SESSION["id_member"] = $objResult["id_member"];
      $_SESSION["status"] = $objResult["status"];

      session_write_close();
      
      if($objResult["status"] == "ADMIN")
      {
        echo "<script>
      $.alert({
       title: 'wellcome to admin page',
         content: '',
           buttons: {
             OK: 
      function(){
          window.location.href = 'admin_adduser.php';
         }
          }
          });
        </script>";
      }
      else
      {
       echo "<script>
      $.alert({
       title: 'FDA Search Engine',
         content: '',
           buttons: {
             OK: 
      function(){
          window.location.href = 'data.php';
         }
          }
          });
        </script>";
      }
  }
  mysqli_close($con);
?>