use it the same way as any other property. for example, you can access its properties:
class a
{
var $b;
function a()
{
$this->b = new b();
}
}
class b
{
var $text;
function b()
{
$this->text = 'This is my text!';
}
}
$a = new a();
echo $a->b->text; // outputs "This is my text!"