There are several ways to create WordPress navigation menus. This how-to article outlines the steps required to manually build menus.
By default, WordPress navigation menus are built automatically. Menu items (i.e. links to pages) are ordered by the date and time of page creation – newer pages are listed before older pages.
Following are instructions on how to manually create navigation menus.
Instructions
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.