In order to make Square items visible on your Ordering.app website, you will need to set Publish Online to True within the section Custom Attributes. You may also set Publish Online to False in order to hide items from your online customer-facing site. This toggle is located within the edit item section of each individual Square item.
Please see the following video demonstration of how to publish/unpublish your Square items. In this demonstration I have unpublished the item "Nachos":
Walkthrough of another example!
Currently, my Ordering.app site only displays the following items:
However, I have a Water item that I want to make visible as well. I'll do so by first clicking into my Water item itself in my Square library:
After clicking into this item's individual Edit Item screen, if I scroll about 2/3 of the way down I will see a section labeled Custom Attributes:
First I set the "Publish Online" toggle to True:
And then I will hit "Save". Once done, this item will now appear on my Ordering.app website!