As I understand it, it allows documents to be stored on a server so that multiple people or groups can access the documents. It allows for more efficient collaboration on a document than simply emailing it around. Does that make sense? We've been using a similar technology (Sharepoint) at work for years. But we are within the same network. This allows sharing by anyone with access to the internet, really. They would just have to be given permissions.
Again, this is just my understanding, never having actually used it.