The right-hand column looks cluttery and confusing to me. It needs more visual distinction to work, maybe a colored background.

Can I turn it off? Is it configurable? What are the configuration options?

You can remove all existing blocks in the right sidebar (using the Block Manager) and that will remove the sidebar completely.

There are no configuration options specifically for that area, though, it is part of the responsive Theme.

You can change that to look however you wish with a custom Theme, of course.