Navbar / Nav Menu
The Navbar links are determined based on the NationBuilder pages that are ticked "Include in top nav". These pages can be seen in the control panel here:
#Relevant Page Tags
nav_hide
If a page is "included in the top nav" but you don't want it visible in the topnav (common to hide "Home" from nav since logo links or if needed in top nav for sitemap.md purposes) you can remove it from the navbar by adding page nav_hide.
site_header_fluid
By default - the nav logo and nav items are restricted to container width. You can add tag site_header_fluid to instead have it in a container-fluid (no width restrictions). This is helpful for navbars with lots of links or ones when lengthy titles are used.