Edit existing topology in Zbrush

This is a short demo showing how to take existing geometry and to edit the geometry/topology to better suit your mesh needs.
Load a Zsphere.
Scroll to the "Topology" dropdown.
Click "Select Topo" and choose your geometry to be edited.
Go to the "Rigging" dropdown above and choose "Select Mesh" and choose the mesh your editing (to be used as a surface that you can lay your verts onto).
Click the "Edit Topology" button and begin editing the topo.

Tips.
Hovering over the verts will turn your brush green, you can then click on that vert to use as a starting point.
To reset the beginning point of your vert placement, double click in space, otherwise it will start at the center of your zsphere.
Make your draw size about 1-3 so you are only effecting one vert at a time.
This method can also be used to merge two tools, once they have been merged down to one.
Also great way to add geometry to a sculpture without having to venture out to another program.

Edit topology in Zbrush from Nick McGavern on Vimeo.