This article fits all WordPress themes.
Before building your custom menu, you need to create your pages first, then navigate to Appearance > Menus, it is recommended to create your Menu from Pages or Custom Links. Check the video tutorial about how to create a simple WordPress menu:
Tips: don’t forget to pick up the “Primary Menu” option.
If you want to create the sub-menu, you could drag the menu item to edit the menu level, check the video tutorial:
Read more: https://codex.wordpress.org/WordPress_Menu_User_Guide