The same two documents that ship inside the package, readable here without buying anything first.
Five steps from an empty scene to your first outline. Read this one first — it is short on purpose.
Everything else: the four passes, all ten styles, hard meshes, cutout, merge groups, skinned meshes, the recipes, the scripting API, performance figures and troubleshooting.
Prefer to try before reading? The live WebGL demo runs the full package in your browser — ten chapters, every style, every recipe, nothing to download. Most questions this manual answers are quicker to answer by clicking.