Open the Google Photos app
That’s it! That’s step 1. You need to open the app in order for it to do its job. The Google Photos app on a smartphone is designed to copy all the photos from your phone to your Google account in the cloud. If you never open the app, it can’t do its job.
The very first time you open the app, you will need to set it up with your Google account, and whether you want your photos uploaded in Original Size, or Storage Saver size. We recommend Storage Saver. You should then see a message about the number of photos that are being backed up.