Hover over the CWCCWR at the upper left of the screen, then click on Menus on the pull down.
Make sure that you have selected Main (Primary Navivation), then find the pages you want to add, select, then click Add to Menu. Note that you need to create the page first, then add it to the menu.
Grab items and move them to desired spot on the menu. For sub tabs, indent them under the main tab.
The title will default to the page title. Use the pull down to edit, e.g. to shorten it to fit on the screen.
Click on Save Menu when done.