The navigation provides quick links to key sections of your store. Having a navigation is optional. If you have a small number of products or pages this may not be necessary.
Pages can be added to the navigation on the pages list by dragging and dropping them into the Navigation section or by clicking the toggle button on the "view page".
The order of pages in the Navigation section provides the order the pages are displayed in the navigation itself.
Alternatively when creating or editing a page, just check "show in navigation" to add it.
"Sign In", "Account" and "Cart" will also appear along the top navigation.