Creating topology in zbrush

                             When you are creating a game character you have to make it low poly. If your game character is high poly it may cause some problems when you are importing it to the game engine. Using zbrush topology tool you can create low poly model according to the actual high poly model.
                              In here I use demo head for my tutorial. Open your high poly model and click Make PolyMesh3D. You can find it under Tool.

                       
                         It will create another object which has same poly count. Click on your previous object. Expand the SubTool and click Insert. Select ZSphere.

                         Select the Zsphere in SubTool. Scale it down until it hides from your object. Switch to Draw mode by pressing Q. Expand the Rigging section and click Select Mesh.

                           Choose your PolyMesh3D object that we created in previous step. Then expand the Topology section and click on Edit Topology button. Now you you can draw edges on your object. If you want to delete a edge click on that edge while holding the Alt key.

                           You can preview your low poly object by pressing A. To view it clearly hide your high poly model in SubTool.