The Outliner is a list of everything that is the current Set, Scene or Shot that you are working on.
In the following example of an outliner of Set:
On the RIGHT SIDE of the panel are two buttons: the Options and Close button.
Options - any options for the window. Clicking on this will bring up another panel that can be cancelled or confirmed.
Close - this will close the panel (Hotkey - Alt+1)
Functions of the Outliner
Selecting objects
Overridden