OO usage in code igniter structure, Model, Controller

[eluser]farinspace[/eluser]
I am trying to get into the work flow of codeigniter and would like some practical examples. My one main question is about proper OO usage within models/controllers (please forgive me if im just being dense and the answer is just staring me in the face) ...

Basic example (outside of codeigniter)

Code:

$link = new Link($db,55);

$link2 = new Link($db);
$link2->title = 'link title 1';

$link3 = new Link($db);
$link3->title = 'link title 2';

$link->append($link2);
$link->insert($link3);

echo $link->title;
echo $link->description;

$tree = $link->get();
var_dump($tree);

All the codeigniter model examples I've seen, seem to be more on the concept of a "manager" pattern, instead of managing single objects and having them interact with one another ...

Code:

// inside a controller function

$this->load->model('link');
$this->link->appendLink('link title 1',55);
$this->link->appendLink('link title 2',55);

$title = $this->link->getTitle(55);
$desc = $this->link->getDescription(55);
$tree = $this->link->get(55); // gets tree starting at this links ID/level

Lets say I wanted my model to return an object, how does the model go about creating an instance of another model/class (possibly passing an initialization parameter, and using existing db connection) and returning that object ... all with in the codeigniter framework?