This example will be done using a single page, if you want a redirect after form submit just enter an action and move the PHP over to the new page.
<?php if(isset($_POST['submit'])){
login();
}
?>
<form action="" method="post">
<input type="text" name="username" />
<input type="password" name="password" />
<input type="submit" value="Login" name="submit" />
</form>
<?php
function login(){
$user = $_POST['username'];
$pass = $_POST['password'];
$login = Auth::ProcessLogin($user, $pass);
}
?>