As you are building your site, odds are you will want to change which menu a page lives under. With Wordpress this is very easy to do. You have two options to edit the menu's of the site.
Option 1: When editing the page, on the right hand column under Page Attributes you will see Parent with a drop down. Here you can select which page you want the parent to be. For example if you want the Our Staff page to appear as a drop down under About Us, you will select About Us as the parent.
Option 2: This option will give you more customization how how your menus are set and function. In the left sidebar you will see and option titled Appearance. Click here and a drop down menu will appear. Here you will select Menu. This will bring up a new page where you can easily manage your menu's. From here you can drag and drop pages from the list on the left into the menu structure on the right. If you drop the page in by itself it will be a parent page. If you put it under an existing page and drag to the right, it will indent and become a secondary page. You can repeat this step to create tertiary pages also. If you would like the same page to appear in multiple places, once you have placed the page, go back to the left sidebar and drag the page to another place.