Grid Market horizontal navigation bar not showing by default

Hi, I'm relatively new to WordPress and a a CSS beginner (I can tweak if I know what I'm looking for). I've just installed the latest version of Grid Market (chosen because of all the options without the need to edit stylesheets etc), but for some reason the horizontal navigation menu isn't showing in the header under the logo/text by default as shown in screenshots/demo: http://wp-ecommerce.org/

What have I missed? Can anyone help. Thanks!

P.S. I notice the nav bar doesn't appear in these screenshots http://theme.brellabee.com/gridmarket/