I’m very new to Zbrush and I’m trying to sculpt in HD. I watched the video tutorial on HD Geometry but I came across a problem. In the video it tells you to select the HD Geometry sub menu, but mine doesn’t show up. I have a character and I appended subtools and I realised that the HD Geometry option only shows up when my eyes subtool is selected but it disappears if I select another part of my character. Why is this? 
HD sculpting requires a polymesh. If your model is a primitive (parametric) object like the Sphere3D or is ZSpheres, it won’t be a polymesh and so HD won’t be available. Either use Tool>Make Polymesh 3D or (in the case of ZSpheres) Tool>Adaptive Skin>Make Adaptive Skin. The HD feature should then be available with the new object.
Hi thanks so much that totally makes sense now:)
I have one last question I’m not sure where I’m supposed to post it but here goes: My symmetry is way off. if I select symmetry on then the two symmerty squares aren’t symmetrical. The one is always higher than the other. I know that I have probably done something wrong in the creating process because when I sculpt on a preset mannequin then the symmetry is perfect. Any ides what I could possibly have done wrong? All I did was create something with Zspheres then turn it into an adaptive skin and polymesh. I assume I did something wrong with the Zspheres?
Thanks