SWC usage - stage items not available

You might find this thread helpful.

The upshot was that the person asking the question was using a SWC where the symbols in the SWC had an AS Class, and they were referencing that Class in the Class field instead of the Base Class field. The reason this was a problem is that, in order to instantiate that same Class, there has to be an import statement and the import statement points directly to the AS file and knows nothing about the library symbol in the SWC and whatever objects you've put there.

then import it

How do you import it? Generally the only thing you have to do is linking to the swc in the File>ActionScriptSettings>LibraryPath.

Where do you add the items to the stage (where do you call the actuall addChild() code)?