This is a 3D drawing app. More to the point, it's a 3D drawing app for people like me who have no artistic talent at all. It makes every other drawing/sketching tool I have look really, really lame.
Start from a model
You start by selecting a 3D image from their library (you can also select just a cube, sphere or torus).
Flip it around
Once the image is selected, you can rotate it, spin it around, turn it upside down - it's all very easy to do - just keep your fingers or stylus off the image itself and you'll quickly get the hang of what you need to do to orient your sculpture as you want it.
Sculpt and mold
After that, you can use tools (shown on left) to shape, cut and add to the sculpture. As you first touch each tool, a description of what it does appears briefly on the screen, but a bit of experimentation will help you understand. You can adjust the size and "strength" of the tool - how deep it cuts or how much material it adds, effectively.
Impressive 3D views
If you gouge out a little from the cheek as I did here, you'll see that rotating the view now creates appropriate shadows.
Can you believe it?
Is that cool or what?
Oh, I know that all might be old hat to some of you. But really: did you ever think you'd see it in a 99 cent program running on something that weighs under 2 lbs? C'mon, I bet you have never seen anything close, right?
123D Sculpt from Autodesk. Cool beans.