You can use Craft Designer to register items.

To display an item on the order screen, you need to register and edit the item using Craft Admin and then set it to public.

This section explains the required and optional settings for registering items. See the following for more details on making settings.
Required Settings
Set the basic information for items handled in the store.
You can also manage multiple items using functions such as copy, delete, and change the display order of items.
Optional Settings
You can set detailed information about items and make display settings on the order screen.
The default display language depends on the OS language setting.
