Prior to the latest update to the Chrome OS version of the Google+ Photos application, backing up pictures that you had taken to Google+ Photos required a little more effort. You first had to open up the Google+ photos app and initiate the upload so they would backup, now that is all over as the update makes it so an auto backup feature runs in the background at all times. If you use a Chrome OS based device whether that be a Chromebox or a Chromebook, simply plugging in any external storage and uploading the photos to the Chrome OS device will promptly send those photos to the Google+ Photos application. It's that simple.
With things running in the background it's just as easy to back up your photos automatically on Chrome OS now as it is on an Android device compatible with the app. Auto backup can be turned on or off as a feature that runs in the background on the device so that any photos taken with the devices camera are automatically backed up to Google+ Photos. It's good to see some of the features that we use on Android first come to devices running Chrome OS as well. The background feature works with videos too of course, so there shouldn't be any worry about losing any home videos of the latest family gatherings.
Updating the application should happen just as automatically as the backup of your photos and videos, assuming you have a connection to the internet. If you don't, then the app will simply update the next time that it links up to a connection, wherever that may be. You can also be proactive about the update or check to see if you have the latest version with the auto backup feature already by navigating over to the Chrome web store and seeing what version of the app you have on your Chrome OS device. The version of the application that you're looking for here is 1.288.0, so if you have a version earlier than that you won't have the auto backup feature available to you just yet. It should't take too long to get it on your device, but in the meantime you can always back them up manually.