Create External Navigation Links
You'll generally want most (if not all) of the links in your site's navigation to link to a page within your own site. But there are some situations where you may want the navigation to link elsewhere - to lead people to your twitter page, an outside blog, a partner's site, etc.
To create a navigation link that leads to another site, go to the Pages tab, click the + Plus button, and choose the External Link option.
Give the link a name; this name is what will appear in your navigation. Then enter the full link to the page or site to which you want to link. Then click Save.
Now if anyone clicks the link to this page in your navigation menu, they'll leave your site and go straight to the link you created above. If you ever want to remove the link and turn the page into a normal page again, just replace the external link with a standard page.
You can do the above with any page on your site aside from the Home page.