Web 2.0 - Google Docs

I have begun using Google docs this week. I thought I was doing pretty well - I setup a couple of documents and tested them out - they worked great. I then got fancy and applied priv's to one of the folders bia a Google Group - or so I thought. Imagine my surprise when a new document showed up from Cyn in the shared documents. I am not sure how that happened - but it shows that I don't quite understand the security involved with the documents. If anyone can help me understand how to share a folder vs. a document, that would be great. I have resorted to reading through the help - so if I find an answer, I will be sure to post it!