Welcome to the Community, Larry! 
You can maintain multiple groups of subscribers in your list using tags and segments. A tag is essentially a field that you would be applying to your subscribers, and a segment is a search for subscribers that you can save based on different criteria, including tags.
Using tags and segments allows you to send Broadcast emails and Campaign emails to subscribers based on their tags.
I recommend taking a look at this Community post that goes into further detail about how you can manage your subscribers in one list with tags and segments.