How to create a submenu in WordPress
📝 Note: Please note that this guide refers to classic themes. If you need to add subitems to FSE themes, here is a useful guide.
Submenu items are secondary menus that appear beneath the primary menu items, used mainly to organize related content for an efficient experience.
Navigate to Appearance > Menus.
Select from the dropdown list the menu that you want to edit.
From the Add menu items area, check the subitem and click on Add to Menu.
After adding it, choose the subitem and drag it under the primary item.
When everything is ready, click on the Save Menu button.
📝Note: If you want to make the menu items more suggestive using menu icons, check this doc.