There are a few different ways you can handle your WordPress navigation.
By default, the navigation menu is automatically built. The order is based on the order in which the pages were created.
You may also manually create menus. This how-to article outlines the steps required to manually build your WordPress menus.
Instructions
To manually build a menu, locate APPEARANCE -> MENUS in the left column of the admin area.
Create a new menu on the right. Enter “Main Menu” or whatever you’d like to name your menu (note: the menu name will not display anywhere on your site), then click Save Menu.
Drag and drop your existing pages and/or posts to your new menu. You may add links to other website pages by using Custom Links which is located below your page and post listings.
Once you have added and arranged your menu items, click Save Menu.