Sculptris is a 3D character modelling tool with a difference: anyone can use it. You don't have to understand complex technical jargon, or explore endless dialogs to get it working: it's actually possible to create something interesting in minutes, even if you've no modelling experience at all.
The key to this simplicity is the Sculptris interface, which is perhaps as close to sculpting as you'll get on a PC. Launch the program and you're presented with a clay ball; click and drag with the mouse and you'll deform the ball accordingly - it's all very intuitive.
An interesting plus point is that the program mirrors your work on the other side of the ball. So if you start by forming an eye, for instance, then the second will automatically appear. Add a nose and mouth and you've created your first basic 3D character, all in a few seconds.
There are plenty of tools to vary how the sculpting process actually works, options like Flatten, Grab, Smooth, Pinch and Inflate. But again, while these are tweakable, to a degree, there's no great complexity here, and you'll probably learn by just "doing": selecting an option, trying it out and just seeing what happens. It doesn't matter if you make a mistake, an Undo option will quickly reverse your last steps.
There are more advanced options, if you need them. You can sculpt with a range of different materials, for instance; paint on your model to add colour or texture; or maybe import a model as a starting point (Wavefront OBJ files are supported). While none of these are too complicated, Sculptris has little in the way of built-in help, so if you run into a problem you can't solve then we'd recommend checking out the Sculptris forum for advice.