You can easily download and install apps on your Android Mobile phone that are not officially available in the Google Play Store including apps that have not been approved by Google yet.
The Android App developer will offer the app as an .apk file - think of this as the .exe installers that ship with Windows software or .dmg files of Mac – and you just need to open that file in your Android Phone to install the app.
However, there’s one change that you would need to make to your Android phone before installing .apk files directly.
Open your phone’s Settings app, tap Apps and Notifications > Advanced > Special App Access > Install unknown Apps and here choose the app (like your Chrome web browser or Gmail app) that you are using the download the APK file.
Tap the app name and check the “Allow from this source” option to permit your phone to install apk files download from this app.
Now open the APK file again and follow the onscreen prompts to install the app on your phone.