This is a tutorial on how to install an app from Google Play which has been shared for internal testing.
This means the app is not yet published in the Play Store. This feature is mainly used by developers to quickly share their newest version with some testers (usually by sending out a link). In order to be able to install these internally shared apps you will have to allow this on your device. It's nothing to be afraid of and very easy to accomplish. Also you will have to do this only once. Just follow this guide.
Okay let's open the Play Store link on the builds page.
If you have a previous version of the app installed then please uninstall it before installing the new version.
Hint: If you have access to WiFi you should use it to save your mobile data for more important things.
If app sharing is disabled then your device will show this warning. Tab on the "Settings" link in the text. If that does not take you to the Google Play settings then open the play store and access the settings from there.
Scroll down to "Play Store version". and tap it 10 times (until the countdown reaches 0). Congratulations you now have access to the developer settings on your phone. This is nothing to be afraid of. It simply shows you more options in the settings.
Now you can see the previously hidden "Internal app sharing" option. Turn it on.
Return to the Play Store. If the install page is not shown then just follow the link on the builds page again.
Now you can hit that "install" button. Hit it again in the dialog that follows.
Now you can finally open the app.