I'm Exhausted - Give me a hand here!

[eluser]taewoo[/eluser]
I suggest you watch the codeigniter tutorials... these are really really basic questions.
You need to pass the variables from your controller to your model. Just like you would in regular, non-MVC php app.

Code:

$this->load->model('your_model');
$result = $this->your_model->get($category, $city, $letter, $page);