You need to create a fabric listing first: please go to Stash, and click the link "Add new".

You can fill out the fabric information there, and set privacy of the photos - in case the fabric is set to private, the photos will be replaced by a key icon.

Photos can be only added to a fabric listing that already exists, so you may filter stash by "My stash" and then click the small pencil icon to edit a listing. Once there, please go to the second tab (Files), and upload the photos :)

Hope this helps!