If you didn’t set up iCloud Drive when you installed iOS 9, you can set it up in Settings > iCloud. iCloud Drive is an upgrade to Documents & Data. When you upgrade to iCloud Drive, your documents are copied to iCloud Drive and become available on your devices using iCloud Drive. You won’t be able to access the documents stored in iCloud Drive on your other devices until they are also upgraded to iOS 8 or later, or OS X Yosemite or later.
Set up iCloud Drive. Go to Settings > iCloud > iCloud Drive, then turn on iCloud Drive and follow the onscreen instructions.
Show the iCloud Drive app on your Home screen. Go to Settings > iCloud > iCloud Drive, then turn on Show on Home Screen.