Untitled

use SSL / https on page
<html>
<body>
   <form action="b.php" method="post">
      <input name="username" type="text" />
      <input name="password" type="password" />
      <input type="submit" />
   </form>
</body>
</html>

<?
$sql = "SELECT * FROM user WHERE username = '{$_POST['username']}' && password = '{$_POST['password']}'";

if (....) {
    $_SESSION['logged'] = true;
    header('location: a.php');
    exit;
}
?>