It syncs everything to cloud storage (via your Google account), but nothing gets shared publicly unless you want it to be. Like if you wanted a friend to look at something, you'd have to go through Drive, say you want the file to be public, then get the link. Otherwise only you can view your documents.

You should be able to use it offline too, and have it sync only when you have web access again. Then you can get to your documents from anywhere that you can sign in to Google.