Go to Appearance >> Menu. Create and save a menu with your desired links. For a full video tutorial on navigation menus, please click here.
Primary navigation menu: This is the menu to the left of the site title/logo
Secondary navigation menu: This is the menu to the right of the site title/logo
Mobile navigation: This is the menu that replaces the primary & secondary navigation menus on mobile devices
Make sure you have a mobile navigation menu enabled. If you don’t, not only will your visitors not be able to browse through your site on their device, you’ll get a random bunch of links in a weird location under the logo.