Easiest way: in "tools" menu go to "customize". In the window that oppens
choose "commands", in categories choose "view", in commands scroll till you
find the "outline" button, click and drag it to some place in one of the
toolbars. If you do just that, than close the window, the button will be
there every time you oppen word. One click on the button and the toolbar for
outline pops up lika a "floatting toolbar".
If you want to take this one step further, before you close the window
choose "toolbars" and click the square before the "outline" toolbar. It might
be convenient tha to click and drag the "outline" button to this toolbar. The
options on the bar are "activated" in "customize" mode. They will be
deactivated otherwise, untill you click on the outline button.
Hope it helps!