, Please 
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Maybe you've seen my other tutorials...or my signature..
Anyways I'm going to show you how to make a system so users of your site could register accounts and you could have protected - user only - pages on your site
Ok, so we start by creating a config.php file.
<?php
$dbhost = 'database host';
$dbname = 'database name';
$dbusername = 'database username';
$dbuserpass = 'database password';
mysql_connect ($dbhost, $dbusername, $dbuserpass);
mysql_select_db($dbname) or die('Cannot select database');
?>
Fill in the values of your host and upload it.Here are querie to run in PHPmyadmin
CREATE TABLE `users` ( `id` INT( 11 ) NOT NULL AUTO_INCREMENT , `username` VARCHAR( 255 ) NOT NULL , `password` VARCHAR( 255 ) NOT NULL , PRIMARY KEY ( `id` ) ) TYPE = MYISAM ;
Next, lets create index.php.
<?php
//start the session so you would stay logged in
//always must be on top
session_start();
//include config.php file
include('config.php');
?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>The site</title>
</head>
<body>
<center><a href="?p=idx">Home</a> - <a href="?p=page">Protected page</a>
<?php
$p=$_GET['p'];
//see my ?id= browsing tutorial
switch($p){
default:
//if user isn't logged in lets show him the log in form
if(!isset($_SESSION['username'])){
?>
<form action='login.php' method='POST'>
Username: <input type='text' name='username'><br>
Password: <input type='password' name='password'><br>
<input name="login" type="submit" value="Submit"><br>
Not <a href="register.php">registered</a>?
</form>
<?}
else{
//$_SESSION['username'] = the current users
//username. It will be echoed like "Hi, user!"
echo "<br><br>Hi, ".$_SESSION['username']."!";
echo "<a href='logout.php'>Log out</a>";}
break;
case 'page':
//you can use it like this or use include()
if(!isset($_SESSION['username'])){
echo '<br><br>Log in to see this page!';}else{
echo '<br><br>Only user who is logged in can see this!..and you see this so this means you are logged in;]';
}
}
?>
</center>
</body>
</html>
You see the explanations in the code.Now we need a file that will log the user in, right? Right!
Create a file called login.php
<?php
//start session and include conf...
session_start();
include'config.php';
//get the variables from form and adding some little security
$submit=$_POST['login'];
$username = mysql_real_escape_string(strip_tags(htmlspecialchars($_POST['username'])));
$password = md5($_POST['password']);
//if submit button is pressed
if ($submit){
if((!$username) || (!$password) || ($username=='') || ($password=='')){
header("Refresh: 2;".$_SERVER['HTTP_REFERER']);
echo'<center>Please enter both - username and password!</center>';
}
//lets see if the user exists by making a query which selects
//submitted username and password from the database
//and the we use mysql_num_rows() to count the results returned
//if there is a user with a username and password like that $c will be 1
//as it will be counted otherwise it'll stay 0.
$sql=mysql_query("SELECT * FROM `users` WHERE `username` = '".$username."' AND `password`= '".$password."'") OR die(mysql_error());
$c=mysql_num_rows($sql);
if($c>0){
$r=mysql_fetch_array($sql);
//set $_SESSION['username'] to the username from database
$_SESSION['username'] = $r['username'];
header("Refresh: 2; url=index.php?i=idx");
echo'<center>Login successfull!</center>';
//else, if there werent any records found show an error and
//return the user to index.
}else{
header("Refresh: 2; url=index.php?i=idx");
echo "<center>You couldn't be logged in!</center>";
}}
?>
Ok, so the user is logged in, everything's fine ...but uh-oh...how can user log in if he's not registered ?
make a file called register.php
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Register!</title>
</head>
<body>
<form action='<?=$_SERVER['PHP_SELF']?>' method='POST'>
Username: <input type='text' name='username'><br>
Password: <input type='password' name='password'><br>
<input name="register" type="submit" value="Submit">
</form>
<?php
include('config.php');
///variables...
$submit=$_POST['register'];
$username = mysql_real_escape_string(strip_tags(htmlspecialchars($_POST['username'])));
$password = md5($_POST['password']);
//if button is pressed
if($submit){
//if username is not blank..same for pass
if(($username) and ($password) and ($username!==NULL) and ($password!==NULL)){
$sql="INSERT INTO `users` (`id`,`username`,`password`) VALUES ('NULL','".$username."','".$password."')";
mysql_query($sql) or die(mysql_error());
echo "Congratulations! You are registered!<br><a href='index.php'>Log in</a>";
}
}
?>
</body>
</html>
and the logout.php<?
session_start();
$_SESSION = array();
header("Location: index.php");
?>
I'll add some more explanations later...don't have time now sorry.
But you have the code...and if you have questions - ask.
Preview
when u dont get it say it, dont really know how to say it in english 
