Rainier - Navigation Menu
To add a menu to your blog, navigate to Dashboard > Appearance > Menus and click on “Create a Menu.”
Select the items you wish to add to the menu, and click “Add to Menu”. Drag and drop the items into the order you wish them to appear. "Tabbed" items will become drop-downs.
Assign the menu to a Theme Location at the bottom of the menu. In the Rainier theme, the top / sticky navigation is the Header Menu. The Footer navigation will display to the left of the site footer credits.
More information on setting up the menu can be found here.