ZSpheres is a technique, unique to ZBrush, which allows us to create a model from scratch directly inside ZBrush. You'll see that this is a very fast way to rough out a model. As ZSpheres have a round shape, this technique is especially useful for organic forms, like a tree or a character, but less useful for modeling more straight forms like a building.
In the first chapter, we discussed different workflows of creating game models. For our first one, we'll mainly rely on ZBrush, as the following image shows: