Hi,

It's sidebar place. 

If you want to hide the sidebar, you can go to Customize > Single Posts > General > Single Posts Sidebar Layout > and select "No Sidebar with Container Width Smaller" or "No Sidebar"

If you want to put the widgets to the sidebar, you can go to Appearance > Widgets > drag & drop widgets to "Main Sidebar" and config it.

Best Regards,

PenciDesign