This tutorial will show you how to only select one side of the mesh when working on a sculpt within Zbrush.
Sometimes when working on a sculpt in Zbrush you only want to affect one side of the mesh and not the other. In the tutorial, Rowena makes use of the Backface Mask button which is perfect for this.
It can be found under the Brush > Auto Masking > Backface Mask dropdown in the top left of your screen.
Check out some of the other great tutorials on CGHero.