Drop box does NOT access your files on ANY device but is a cloud based server repository. What it is a mounted folder on a networked remote server,and that is visible in Windows Explorer (PC) Finder (Mac OSX) and an App on iOS devices.
All your other folders on your PC/Mac remain invisible to Dropbox by default.
When you sign in to dropbox on any of these devices the contents of the remote folder can be viewed as if it were a local folder on your computer harddrive.
You can drag and drop or save directly to the folder from any Windows or Mac Programme through the save as/Export commands.
On the iOS device click on the Dropbox app and you are presented with all your documents in the remote server based folder.
On the IOS device these can be viewed within the Dropbox app or opened in another app.
Documents created in say iOS pages can be shared and sent to Dropbox by tapping the spanner/Share and Print/Open in another App
Tapping format (Pages/PDF/Word) to export in
Tapping choose app radio button Open in Dropbox /Save.
If you have an iCloud account and OSx 10.8 Mountain Lion iWork documents can be saved/swapped Directly within each device automatically.
In earlier OSx or Windows PC versions you need to use your Web browser on your PC/Mac to up load/download documents to the cloud storage for viewing on your iOS device.
You can also add some functionality with Pages by using Webdav services to actually mount the dropbox folder directly within iOS Pages- This has a cost of a few £/$/€ per month from the host.
Suffice to say there are Many ways to share/sync content !
