After you create or load a group, you can modify it. You can modify a group within a project (or family) using the group editor, or you can edit the group externally.
The group editor allows you to add elements from the project view, place additional elements in the view which are then automatically added to the group, remove elements, create attached detail groups (for model groups), and view group properties. When you edit a group using the group editor, the background color of the drawing area changes. The background color is ignored when you print from the group editor.
When you edit a group externally, the group opens as a Revit project file (RVT) or a Revit family file (RFA), depending on the environment from which you open it.