Sessions in PHP (user login)

Question

Im pretty new to PHP and am stuck on how to use sessions to check a username and password against a database.

I have a PHP file call createuser.php which allows me to add users to a database with a username and password from a html textbox. I have another file called viewuser.php which lets me type in a username and password and see if that user/password exists in the database.

How could I add sessions to checkuser which only lets the user use that file if the username and login is correct and is in the database.

Belor if my checkuser.php file.

<?php
 $username = $_POST['username']; 
 $password = $_POST['password']; 

 $db= new  PDO('sqlite:test2.db'); 
 $query = "SELECT * from login WHERE username = '$username' AND password = '$password' ";
 $results = $db->Query($query)->fetchAll(); 

 foreach ($results as $arow) {    
 print 'username: ' . $arow['username'] . '  password: ' . $arow['password'].'<br>';
 }

 $rowcount = count($results); 
 print "number of rows $rowcount <br>" ; 

 if ( $rowcount  > 0 ){
  print " details matched atleast once <br>";
 }else{
  print " details did not match <br>";    
 }
?>

 <form action='' method=post> 
    Username <input type='text' name='username' /> <br>
    Password <input type='text' name='password' /> <br>
    <input type='submit' value='Submit' /> 
 </form>

Answer 1

Here is how

....
$rowcount = mysql_num_rows($results); 
if ( $rowcount  > 0 )
{
 session_start();
 $_SESSION['user'] = $arow['username'];
 print " details matched atleast once <br>";
}

else
{
  print " details did not match <br>";
 }

 ?>
 ...

And in every other page

<?php
   session_start();
   if(!isset($_SESSION['user']))       
      //redirect to login
    else
     //logged in