ar81 has some useful tutorials. This first one is for spacecraft, not spacecraft3, but the principoles are the same. You just need to read the sc3 instructions to see the deltas.
[ame="http://www.orbithangar.com/searchid.php?ID=2747"]Tutorial: How to use Spacecraft.dll (Lesson 1)[/ame]
This is ar81's "advanced concepts" tutorial. I haven't messed with this one myself, yet.
[ame="http://www.orbithangar.com/searchid.php?ID=3640"]Tutorial: Spacecraft3.dll advanced concepts[/ame]
sc3 is super easy to use. Building the mesh is more difficult, and labeling all the mesh components for thrusters and animations is more tedious still, but MeshWizard helps with that.