Terms in plain English:
By adding your wedding on PromiseWeWill.com, your wedding will be publicly listed on the iPhone and Android apps. As weddings are public occasions, we feel that this is not unreasonable. Any user of the app will be able to view your Order of Service (if you upload one) and see where your ceremony and reception will be (if you add this information).
The photos feature is designed to allow your guests to take photos and upload them. To prevent a random user of the app from uploading photos, the user must log in via Facebook first. However, any user can view the photos that have been uploaded.
That's about it!