In ZBrushCore, there are two main types of models:
SubDivision models and DynaMesh models.
To start with, I have ZBrushCore loaded and two dogs in the scene.
The blue dog is a SubDivided model.
If I have the blue dog selected, I can go to the Geometry tab
and you will see he consists of three SubDivisions.
I can scroll up and down his SubDivisions to get the lower resolution version
or the higher resolution of the dog.
The red dog is a DynaMesh-ed dog.
This dog consists entirely of ZBrush's digital clay.
DynaMesh lives in the Geometry tab under the DynaMesh area.
You can see this dog has DynaMesh active and has a resolution of 512.
Both models allow you to achieve a sculptural result in ZBrushCore.
Some things you cannot do with SubDivided models, you can with DynaMesh,
and some things you cannot do with DynaMesh you can with SubDivided.
Let's look at the SubDivided model.
Let's say I want to pull some shapes off the back of the model.
I go to the bottom and select the Move brush, and hold down S to get a larger Draw Size,
and then I start pulling his back out a bit, like this.
You will notice that I get this stretching with the mesh,
since I am pulling the topology of the model up.
If I come back to the blue dog and select the ClayTubes brush,
select a small Draw Size then sculpt from the dog's neck to the back,
you will see that stroke depreciate.
This is because when I pull the surface out, I stretch the polygons that make the model.
With the SubDivided model you could attempt to smooth this out
but you are restricted to how many polygons are in that area.
Come to the Geometry tab and divide this up again to increase the resolution of your mesh
and this will then come through and start smoothing out that area.
However when you do this you increase your polygon count.
If you make large changes to a SubDivided model,
you have to divide the model quite a bit to increase the topology in those areas.
If I do the same to the DynaMesh dog, I am just going to pull his back up.
When I get to those stretched areas,
I can just hold Ctrl and drag off the model, release and it will re-DynaMesh that mesh.
This will give me even topology across that surface.
I come in with a small Draw Size and smooth brush,
and the ClayBuildup brush and get a consistent stroke all the way.
DynaMesh's main function is to generate forms and silhouettes on your model.
If you have an established silhouette, you can bring it into ZBrush,
then SubDivide it and sculpt on it, like the blue dog.
Another option the DynaMesh allows but a SubDivision model will not,
is the ability to use Insert Mesh brushes.
If I select the IMM Primitives brush and drag this out on the DynaMesh dog,
I can insert these shapes.
If I select the blue dog and try and drag this out,
I will get a warning that the mesh is composed of multiple SubDivisions.
You have to delete the SubDivisions on the model to use Insert Mesh Primitives
or convert this model to a DynaMesh.
Another thing that DynaMesh has that a SubDivided does not, is the ability to fuse.
With my dog and those Insert Mesh objects, if I re-DynaMesh this mesh now,
it will take those Insert Mesh objects and weld them to the surface of the dog.
If I smooth these out, you can see they are fully attached.
If I was to take a Primitive and append it to the SubDivision dog,
the SubDivision Dog and the Primitive would remain separate geometry elements.
Another positive of a SubDivision model is you can always switch to a lower level.
If I go back to the blue dog and switch down to SubDivision level one,
I can use the Move brush to move areas on the model to change its shape.
As you can see, as the model consists of lower resolution geometry,
I can easily make these changes here.
I can make his neck wider very easily.
If I go back to the DynaMesh version.
Since this model contains a lot of polygons to handle sculpting,
if I try to manipulate the neck and make it larger, it will take longer.
This is because I am dealing with more polygons in this area.
I am also not going to get as clean a result as I affect tiny areas with the Move brush.
Compared to the DynaMesh model when I did this move,
I am moving larger chunks of the mesh, keeping that thick shape and other details.
After these changes to the lower SubDivision,
you can go back to the higher resolution and see those changes on the entire dog.
There is no wrong type of model to use in ZBrushCore.
If you want to establish a silhouette or form on your mesh
you would start by using DynaMesh.
After you have your DynaMesh model built out to a certain form,
you can then convert it to a SubDivision.
This allows you to further divide it up and add sculptural details.
This gives you the flexibility of going back down to a lower SubDivision
to change shapes in certain areas.
Experiment with both types of model in ZBrushCore
to find out which type fits your work.