Example of using the Grid system / Preload Scene as a game manager in Unity 5.x.
Note that any Scene can still be loaded from the Unity editor. You need to set the preload scene via the Unity editor File -> Scene Autoload -> Select Master Scene
This 'game' is nothing more than a moving square and a score. Once the square reaches the goal, the next scene is loaded whilst the global state (score & level progression) is maintained.
Based on examples shown here: