Keywords are words people text to receive an auto-response with more information, join a list, or trigger other workflow steps. You can have multiple keywords for different ministries, events, sign-ups, etc.
For example, you might create a keyword, CONNECT, and invite people to "Text CONNECT to (775) 347-7333" to fill out a connect card or sign up to get updates from your church. At the same time, you could also have a keyword, EASTER, that people can text to get more information about your upcoming Easter events or to sign up to volunteer.
Lists are where your subscribers (contacts) are stored. Each keyword can add subscribers to one or more lists. You can have as many lists as you'd like, and subscribers can be in multiple lists simultaneously. People can join a list through a keyword, but you can also add them in other ways like by importing a CSV file or integrating with your church management software.
Note: If you delete a keyword, you will still have the list it was tied to and any subscribers in it.