If you are installing a new ROM, flash the ROM first, followed immediately by GApps before the first reboot.
Google Apps, also known as GAPPS, are a set of applications developed by Google that provide a range of services, including Google Play Store, Google Maps, Gmail, Google Drive, and more. These apps are not part of the official Android Open Source Project (AOSP) and are only available on Android devices that are certified by Google. However, many custom ROMs and Android enthusiasts want to run GAPPS on their devices, which is where this paper comes in. gapps android 7.1.2 nougat