sTile is a program designed to create 'Seamless Tiles'; small images that, when lined up adjacent with itself, makes a seamless pattern with no discernible borders. It can do other things, but that was (and still is) its primary purpose.  It is based on gradients, the gradual shading from one color to another.  Best results for 3D look is to use a light color and a dark color for the gradient.  After the gradient, there are numerous 'filters' and 'distortions' that can be applied to the image to alter the appearance in a variety of ways.

It's difficult to actually draw anything with this program; but it can create some pretty colorful images, as you can see from the examples on these pages.  Most of the time, you won't start out with a specific result in mind; it's more of a creativity exploration tool.  You just start playing with the various settings until you stumble upon a combination of things that looks cool.  Save the image, and start over.