There are two types of Department Groups: Station and Organizational. 

Station groups have a physical address they relate to specific locations a user is located at or responds out of. They should represent a physical response location, or the location of where personnel/apparatus will stage or are housed. Station Groups can also be responded to as a detail. Users of the Resgrid Responder app or the Resgrid Unit app that are responding to a station which will generate ETA's.

Organizational groups do not have a physical address, and users cannot select an organizational group to respond to. But Organizational groups can be sub-groups of existing groups. For example you have a top level group (Station or Organizational) with multiple Organization sub-groups under it. This can allow you to segment users under other groups.