There are several topics in the Programming with LiveCycle ES2 at http://www.adobe.com/go/learn_lc_programming_9.
Try this link: http://help.adobe.com/en_US/livecycle/9.0/programLC/help/index.htm?content=001386.html#154 8277 for a tutorial/guide.
Hope that helps.
Thank you for all replies, they are very helpful for starting to learn more about DSC.
I do have another question, is it possible to re-write an already built-in service to customize it in a different way. e.g. The Service Operation "Read Document" in Foundation > FileUtilsService to accept a different type of its Input?
That would only be possible if you had the source code for the original DSC. I believe Adobe does give it out for some components as examples/samples, but not for all.
If you don't have the source, then you'll have to add a new DSC to add your functionality.