Gotcha. You're "blog posts" page is an author archive page. Here's what you should do:
1. create a new blank page called "blog".
2. click on "menus" under appearance, and create a new menu called "main nav". Then, add the menu label names and the links to create a custom, top level menu list by using the left-hand column. Add a home, blog, and whatever other tabs you want to the menu. click save menu, and then on the left hand side under primary navigation, select your new menu.
3. Refresh your site. If done correctly, you should see that your main navigation is there.
4. click on "reading" under "settings" from the dashboard. Select the option under "front page displays" as "a static page". Choose the page you want for your homepage, and for the blog posts, choose the page you created called (blog).
That should do it, and you've got a fancy new nav bar to boot!