This tutorial covers how to add more shape sets from the library where they are organized into different libraries based on their most common use (flowchart, org chart, iPhone, etc).
Click "More Shapes" at the bottom of the toolbox, OR
Select "More Shapes" under File in the menu bar.
Check the shape libraries you want to show in the toolbox and click 'Save'.
From the Shape Manager, accessed via "More Shapes," you can also import Visio stencils and SVG files. Simply click the Visio stencil or SVG option at the top of the Shape Manager window, attach the files, and import. These shapes will then appear in the "Custom" section of your shape libraries list, where you can turn them on/off.