If you have a list and would like to have patrons able to choose to opt into that specific list, such as an area of interest, follow the below steps:
On the Marketing lists screen,
1) Create or edit an existing list
2) Choose the checkbox for "public opt-in" and save
The list will now appear on the public pages customer information screen for opt-in by patrons. When they opt in, they are added to that list for future communications on that topic.