Ok, I'll try to walk you through it:

After you've created the additional pages, use your mouse pointer to select the navigation bar in the main editing window. If you're on one of your regular pages, you will only be able to select regular page objects. In order to actually select the navigation bar, you will have to hold down the Control key on your keyboard and left-click on the navigation bar. Alternatively, you can select the "Navigation" layer in the "Pages" panel and then just perform a simple click on the navigation bar in the editing screen.

Once the navigation bar is highlighted, switch to the "Properties" panel and proceed to the "Navigation" section. Here, you will find a list of all the pages that are part of your project. There will an eye icon next to each page. Click on that to toggle the display of the page in the navigation bar.

This should be what you were looking for. I hope it helps.