You are using a custom theme. Can you ask this to the theme dev. or provider? We do not have access to that theme so we cannot diagnose it.
That said, in the Pages editor screen, hover over the page title and select a different page template (if they exist).
To add a sidebar to a page template see:
http://codex.wordpress.org/Function_Reference/get_sidebar
does your theme have any page templates ? there might be a template with sidebar?
– check under ‘edit page’ – ‘page attributes’
what page is the new one?
unfortunately, this forum cannot help much, as you are using a custom made theme; you might need to contact the developer for support.
The theme is Twenty Thirteen. The new page I added is “Shop”.
your theme might remotely be based on Twenty Thirteen (although not even the basic html structure is the same), but the current version looks too far customized for any easy support from this forum.
additionally, your ‘shop’ page is using some woocommerce code – what plugin are you using for that?
have you made a custom template for the page?
if not, what is the full code of page.php in your theme?
