Nirvana is a city separated by rings. The inner rings are controlled by corporations. The outer rings are pure anarchy. But you aren't even in the city of Nirvana yet. You're on the outskirts in an abandoned prison. Make your way in.
In order for you to be able to install this game, you need to enable (allow) installation of applications from unknown sources (Unknown sources) in the phone settings. Usually this item is in the Security section