Horizontal Navigation - classic Classic Google Sites
Classic Google Sites offer two methods of navigation for your site, in the sidebar vertically and header horizontally.
Note: The Google Sites horizontal navigation only offers one level of drop-down menu: you cannot have a submenu that appears as a submenu of the drop-down menu.
For new Google Sites see these instructions: Pages and Navigation - new Google Sites; Nest Subpages - new Google Sites; Add Links to Navigation - new Google Sites
Instructions - Horizontal Navigation
You need to enable this new navigation, to do so use the More button (it looks like a gear/cog), then Edit site layout (or keyboard shortcut Shift+L)
If you need to enable Horizontal Navigation use the Horizontal Navigation button: once used the site header will grow and you can click on the Horizontal Navigation area and the Configure navigation dialogue box will appear.
To add a page from your site use the Add Page link to show the sitemap to pick your page from, or search for the page you want to have in the Horizontal navigation.
If you want to add a link to another website then use the Add URL link to provide the web address and the link text you want to display.
If you want to make one of the links appear in the mouse-over drop-down menus then you need to make this an indented link by using the Indent arrow, the grey arrow that points to the right (you can use the Outdent arrow if you make a mistake, the grey arrow that points to the left).
Choose to show the Sitemap and Recent Site Activity if you wish.
Choose to show your Horizontal Navigation as either Boxes, Tabs or Links.
Use the OK button to keep the changes and then use the blue Close button to make the Horizontal Navigation to return to the site.