All items in your sitemap will appear in your main navigation menu. If you don't want them to, you can set up a page attribute called "Exclude from Nav" and tick this to block that page appearing in your main navigation menu.
You can also set other properties, such as "Exclude from sitemap.xml" and "Exclude from Sitemap".
The first one will exclude the special file from yourwebsite.com/sitemap.xml (a file automatically generated and useful to submit to Google webmaster tools).
The second one will exclude the page from your website's public sitemap yourwebsite.com/sitemap