Confusion on locating and applying s

I'm a newbie. I've tried hard to find an answer to my question before posting anything.

My problem appears here, as one example:

The "Pages", "Archives", and "Categories" appear at the bottom, but I can't figure out why. I want to get rid of them.

I think that I see from the webpage source that this is added as part of "<div id="sidebar" ...> but I don't know what puts that in my page. I don't have a 'sidebar' file in my theme (Chunk, from Automattic). I can't find anything in the template or style sheets that add 'sidebar', and I don't know what file is controlling it.

Any help would be greatly appreciated as I learn my way around here. Thanks.