The Floating Group window is used to track group member's health, endurance, and power levels. Many of the various styles are resizable so you can reduce the amount of screen space taken by the window of your group is not full.
The window will appear when you click on the button labeled "Floating Group" in the Interface Options window of the User Interface.
There is nothing shown when the window is concealed. The window is invisible with no graphics or controls to minimize the amount of memory used. Nothing will appear on the screen when you attempt to activate the window.