There are a few ways to backup and restore your Android. You can use a cloud backup service, such as Google Drive, or you can use an app like Titanium Backup. You can also create a manual backup using the Android Settings app. Furthermore, the SP Flash Tool can also...
What is Stock ROM, Custom ROM and Rooting for Android?
That said, using a Nandroid backup to return to stock is only a short-term option. The backup will restore your old apps and data, meaning that apps you've uninstalled will reappear, and text messages you've since received will disappear. If your Nandroid backup is more than a day or two...