Zoom Out enables you to view larger areas of the map.
There are three different ways to use the Zoom Out tool.
Use the left mouse button and click once on an area of the map you wish to Zoom Out around.
Use the left mouse button and click in an area of the map and while holding the left mouse button down draw a box around the area you would like to Zoom Out around.
If your mouse has a scroll wheel you can Zoom In and Out by rotating the scroll wheel while the mouse cursor is over the map.