Create an HTML section for your navigation bar. In the HTML file for the page you are working with, locate the section you wish to add the navigation bar to. Use a element to contain it as follows ...

Locate the lines for "#navigation" and ".sub-menu". You will want to change the "sub-menu" list item class to float left and display as inline to make this tier horizontal.

Navigation menus not written in HTML (e.g., JavaScript) are also not visible to spiders. Submit a sitemap. Link your sitemap in the robots.txt file, and submit through Google Search Console.