When a story is shared, that is when the real power of TightKnit begins to unfold. A shared story is a place where all members of the family that it is shared with can add, not only comments, but other photos as well. Ever wonder who else has photos of your parents wedding, or even your own? Create a story about that wedding, share it with a family that contains extended family members and ask people to upload what they have! Stories and photos are always private -- only those in that family can participate.
Note that once a story has been shared with a family, it cannot be "unshared".
The "Family" functionality is very powerful. You will both create families and be invited to others. It is important that you be deliberate when creating your own recognizing that these are places that, potentially for years, these people will want to come back and share more memories and stories.
For more on "what is a family", click here.