Save your device's photos and videos to your Google Photos library. This can include photos you take with your device's camera and photos saved on your phone.
What is back up & sync? A backup service: Your device's photos and videos will save to your Google Photos library, including ones you capture in the future.
A feature of Google Photos: Google Photos is separate from Google+ (and you don't need a Google+ account to use the Google Photos app).
Privately stored: Photos and videos backed up from your device are private unless you decide to share them.
Syncing: Changes you make to photos and videos, like deleting or editing, will be reflected across all of your
synced devices.
Change the setting Open the Google Photos app on your mobile device

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At the top left, touch the menu icon

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Select Settings > Back up & sync.
At the top, switch it on or off.
If you don't have this app then download it from
HereThings to keep in mind about this setting:Changing backup settings will affect all apps that use Back up & sync, such as Google Drive.
If you have Back up & sync on, deleting the Google Photos app from your device will not turn it off. To turn off Back up & sync, follow the instructions above.
Optional: Check what's backed up
At the top left of the Google Photos app, touch the menu icon

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Select Photos.
Photos and videos that are not backed up will have this icon

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You can
back up your photos & videos and
restore from google photos website
here