 So, you just want a master division. Not a problem. There are two main methods of division. The first is under geometry and divide. Every time you press divide it will add a new level of subdivision to your object. Now something cool about ZBrush is it remembers what you do on the higher levels even when you go back to change things in the lower levels. So if I create skin pores on level 4 and then decide to change the basic shape of her nose back on level 2 even though we're back on 2 the pores are still there on level 4 which is awesome because it makes it super easy to focus on one layer at a time but have the safety of being able to edit the lower levels of subdivision when you want. As a general rule, level 1 is usually the base shape. Level 2 is where you have the main features like the bones and muscles. Level 3 is where the details like the cloth pins and the tendons get sculpted. And level 4 and up is where the finer details like skin pores and surface textures go. You can travel between the different levels by dragging this bar over here. You can delete the layers below the selection right here or you can delete the layers above over here. If you regret deleting the lower layers and you wish you could get them back there is an option to reconstruct the lower layers with this button. Now there's also a dynamic subdivision mode. This is much more useful for hard surface and low poly modeling stuff with Z-Modeler but we'll get more into that later. For now basically all you need to know is with normal subdivision you won't be able to use trim or mirror or edit single polys without freezing the subdivision levels which can be annoying. But with dynamic subdivision you don't need to freeze anything. You can mirror, trim or poly model with no problem at all. Anyway that's the gist. Hope that helps and as always hope you have a fantastic day and I'll see you around.