Currently Ghost only supports blog posts, according to the roadmap version 0.4 is meant to introduce support for pages, but it seems to be a bit behind schedule. If you know express or even just Node, you can hack your Ghost blog like I did, but that makes it unupgradeable.
In the meantime here is what you can do to avoid that problem:
1) Save a draft
2) Copy its url by clicking the gear icon next to “save draft” button
3) link to it from your template
Now you have a static page which is really an unpublished post hence it doesn’t appear in the blog post listing.
Hat tip jamesramsay @ github