When working with a family in the Family Editor, add a control to a family to easily mirror and rotate the family once it is placed in your model.
Revit rotates or mirrors the geometry about the origin. Single arrows rotate the family instance 180 degrees around the family origin. Double arrows mirror the family instance horizontally or vertically.
You can place the controls anywhere in the view. It is best to place them where it is obvious what they control.
In architectural projects, controls are useful, for example when creating a door family. The double-horizontal control arrows change which side the door is hinged. The double-vertical control arrows change the swing of the door from inside-out to outside-in.
In system engineering projects, controls are useful, for example, when creating a pipe fitting family. The control arrows allow you to flip the fitting horizontally or vertically.