How do I save an email attachment to iCloud Drive from my iPad?

iOS 9 has made it easy to save email attachments to your iCloud Drive (and attach items from your iCloud Drive to outgoing emails), which allows you to access them from all of your devices. To save an attachment to your iCloud Drive, simply long press on the attachment until the Share options come up, then tap on the cloud icon labeled "Save Attachment." An iCloud Drive window will pop up, tap "Save to this location" at the bottom. Now you can access the downloaded files on your iPad via the iCloud Drive app.