Zoom In:
Click the "Zoom In" tool.  A red box appears around the icon when it is enabled  and "Zoom In" is displayed in the lower left corner of the window indicating that it is the active tool.
 
To zoom in on a particular area use your cursor to drag a box around the area.  A red box will appear on the screen outlining the area to zoom in to.
 

The result of zoom in:

 

Or single click a location on the map to zoom in 2x at the point clicked.