Your site's navigation menu is managed separately from your pages, under Navigation in the admin sidebar. Each menu item has a label, a URL, and a sort order.
Linking to page sections
If your homepage has a section with an anchor id (set when you create the section in the page builder), you can link directly to it from a nav item using /#anchor-name — for example /#contact jumps straight to your Contact section.
External links
Nav items can also point anywhere else — another page on your site, or an external URL — and can be set to open in a new tab.