$this->config->get('something') in opencart

I am newbie in opencart as well as in php. I am discovering opencart templates, I found $this->config->get this line, I am a little bit confused about this. I don't understand clearly. I this request we are using this object (current) access config object and call get method of config object, am I right ?

I have read that get query data from database. This data is set from admin panel.



So here are questions :

1. Where can I find config object declaration

2. Get uses simple query to retrieve data from database ?

3. How can I add my own fields, I mean how can I add some fields in admin panel, for instance in category configuration to use them in this way $this->config->get.

I would be grateful for any help.