The old way to create a link to an external site in the main navigation menu was to embed a meta tag which redirected the user to the desired site. Unfortunately, this technique is not 508/ADA compliant. These pages need to be removed and replace with the new, far slicker, link.
To remove the old page, click the page name in the sitemap, then click the Archive button just above the sitemap.
Next, use the Add New menu immediately above the sitemap and select the Link option.
These links appear in your navigation menu but may point to any external website. In the site map, webmasters will see a small "link" icon to distinguish links from pages.
If you create link (or any page for that matter) in the wrong location, click it's title in the site map and then click the Move button.