A new iCloud Drive setting in iOS 9 enables a hidden app that lets you manage your entire file library. You can find the setting at Settings > iCloud > iCloud Drive > Show on Home Screen. After activating it you’ll find a new icon on your home screen for the iCloud Drive application.
At the moment the app doesn’t seem to be loading any content, but obviously that will change before launch. This app will likely function the same way the iCloud Drive folder in the Mac Finder does.