What are the difference between $this->data->total_pages and $data['total_pages']

[eluser]shinokada[/eluser]
Beginner's question.

Could anyone explain the differences between

Code:

$this->data->total_pages

and

$data['total_pages']

My understanding is that the first one is an object way and second way is an array way.

Am I right?

Then what is $this in $this->data->total_pages?

When do I need to use $this->..?

Do I have to use it whenever I use it as an object?

I thank you in advance.