Here’s an interactive tutorial
** Best experienced in Full Screen (click the icon in the top right corner before you begin) **
https://www.iorad.com/player/2289763/How-To-Add-Sub-Items-To-Menu—WordPress–EN-0078-
9 STEPS
1. From the administration panel, go to Appearance and click Menus
2. Click View All
3. Select your submenu items
4. Click Add to Menu
5. Select each item
6. With your mouse, click and drag the item. Make sure there is a little indentation.
6b. Drop
7. Drag and drop the rest of the menu items
8. Move the items in the specific order you want them appering in the menu
8b. Drop
9. When you are happy with the end result, click Save Menu