In Twenty Thirteen, main navigation not displaying on pages other than home page

I’ve installed Twenty Thirteen with no customization (thus far). My main navigation is displaying only on my home page. How do I get it to display on other pages?

Here’s a link to the site in development: https://katharine-online.com/writer. (Note I’ve put main navigation links into the sidebar on pages other than the home page, since I can’t navigation on these pages otherwise. I want to remove the sidebar nav as soon as I can fix this problem.)

Thanks for any help you can give me.