How do I create a page that is linked to from the navbar at the top of my theme
First create a new page and save it. For the sake of example, lets call your new page "Apples". You are using cutline, so you will have to open header.php and locate this:
Directly below that, you will see the code that obviously creates your FrontPage, Archive and About links.
Add this line...
<li><a <?php if (is_page('apples')) echo('class="current" '); ?>href="<?php bloginfo('url'); ?>/apples/">apples</a></li>
...to the existing lines that describe your about, frontpage, and archive pages. Note that where you position the new entry (first, second, third, or last in line)will be reflected in where the new page title appears in the header.
This should give you a new page tab that links to your new page titled "Apples".
I just confirmed on my test box that this does in fact work. I used this version of cutline,
Both the archive and the about pages also worked correctly with no 404's.
... and as suggested by Lenk, you will need to investigate the use of "pretty permalinks".
Best of luck to you.