Adding a Custom External Link to your Pages/Menu Bar

I would like to add a link to an external link that is visible on the top menu bar which would appear next to your About, Contact, etc. pages (as seen in the image below).

https://img843.imageshack.us/img843/7595/68949191.jpg

Is this possible? If so, please provide me with the code & where exactly it would need to be pasted within editor/template pages.

I have only seen solutions for adding text widgets etc. & that is not what I am looking for.

Please & thank you!