how to create make a secure php login script with database password verification mysql

<?php 
function createsessions($username,$password) 
{ 
    //Add additional member to Session array as per requirement 
    session_register(); 
    $_SESSION["gdusername"] = $username; 
    $_SESSION["gdpassword"] = md5($password); 
 
    if(isset($_POST['remme'])) 
    { 
        //Add additional member to cookie array as per requirement 
        setcookie("gdusername", $_SESSION['gdusername'], time()+60*60*24*100, "/"); 
        setcookie("gdpassword", $_SESSION['gdpassword'], time()+60*60*24*100, "/"); 
        return; 
    } 
} 
function clearsessionscookies() 
{ 
    unset($_SESSION['gdusername']); 
    unset($_SESSION['gdpassword']); 
 
    session_unset();     
    session_destroy(); 
    setcookie ("gdusername", "",time()-60*60*24*100, "/"); 
    setcookie ("gdpassword", "",time()-60*60*24*100, "/"); 
} 
function confirmUser($username,$password) 
{ 
    $md5pass = md5($password); 
    /* Validate from the database but as for now just demo username and password */ 
    if($username == "demo" && $password == "demo") 
        return true; 
    else 
        return false; 
} 
function checkLoggedin() 

<?php 
ob_start(); 
session_start(); 
require_once ("functions.php"); 
if (checkLoggedin()) 
    echo "<H1>You are already logged in - <A href = \"login.php?do=logout\">logout</A></h1>"; 
else 
    echo "<H1>You are not logged in - <A href = \"login.php\">login</A></h1></h1>"; 
?>

<?php 
ob_start(); 
session_start(); 
require_once ("functions.php"); 
$returnurl = urlencode(isset($_GET["returnurl"])?$_GET["returnurl"]:""); 
if($returnurl == "") 
    $returnurl = urlencode(isset($_POST["returnurl"])?$_POST["returnurl"]:""); 
$do = isset($_GET["do"])?$_GET["do"]:""; 
$do = strtolower($do); 
switch($do) 
{ 
case "": 
    if (checkLoggedin()) 
    { 
        echo "<H1>You are already logged in - <A href = \"login.php?do=logout\">logout</A></h1>"; 
    } 
    else 
    { 
        ?> 
        <form NAME="login1" ACTION="login.php?do=login" METHOD="POST" ONSUBMIT="return aValidator();"> 
        <input TYPE="hidden" name="returnurl" value="<?$returnurl?>"> 
        <TABLE cellspacing="3"> 
        <TR> 
            <TD>Username:</TD> 
            <TD><input TYPE="TEXT" NAME="username"></TD> 
            <TD>Password:</TD> 
            <TD><input TYPE="PASSWORD" NAME="password"></TD> 
        </TR> 
        <TR> 
            <TD colspan="4" ALIGN="center"><input TYPE="CHECKBOX" NAME="remme">&nbsp;Remember me for the next time I visit</TD> 
        </TR> 
        <TR> 
            <TD ALIGN="CENTER" COLSPAN="4"><input TYPE="SUBMIT" name="submit" value="Login"></TD> 
        </TR> 
        </form> 
        </TABLE> 
    <? 
    } 
    break; 
case "login": 
    $username = isset($_POST["username"])?$_POST["username"]:""; 
    $password = isset($_POST["password"])?$_POST["password"]:""; 
    if ($username=="" or $password=="" ) 
    { 
        echo "<h1>Username or password is blank</h1>"; 
        clearsessionscookies(); 
        header("location: login.php?returnurl=$returnurl"); 
    } 
    else 
    { 
        if(confirmuser($username,$password)) 
        { 
            createsessions($username,$password); 
            if ($returnurl<>"") 
                header("location: $returnurl"); 
            else 
            { 
                header("Location: index.php"); 
            } 
        } 
        else 
        { 
            echo "<h1>Invalid Username and/Or password</h1>"; 
            clearsessionscookies(); 
            header("location: login.php?returnurl=$returnurl"); 
        } 
    } 
    break; 
case "logout": 
    clearsessionscookies(); 
    header("location: index.php"); 
    break; 
} 
?>

so now you should have three files, if you don't know how to save them, you can use notepad just copy and save them with notepad. then upload to your website which has PHP on it and that's it.