Set up a Google Account (or know your Google Account information First.)
Make sure you have the Google Drive App on the device.
On your device (iPhone or iPad):
  1. Open the Google Drive app .
  2. Tap Menu .
  3. Tap Settings > Photos.
  4. Tap Auto Backup.
  5. Next to "Auto Backup," turn it On or Off.

If you have a lot of photos it may take a while to get them all backed up to your Google Drive account....