Creating the level
Start by opening the GameScreen scene you created earlier by double-clicking on it. There should just be a Main Camera and nothing else. Make the background color of the Main Camera black, just like you did earlier, and set the position to X: 3, Y: 6, Z: -10.
Prefabs
A prefab is a type of asset, a reusable GameObject that is accessible from the Project panel. Prefabs can be added into any scene, multiple times per scene. When you add a prefab to a scene, an instance is created of it. All prefab instances are linked to the original prefab. No matter how many instances exist in your project, when you make a change to the prefab, you will see the change applied to all instances of it.
Creating a Prefab
In order to create a prefab, drag a GameObject that you've created in the scene into the Project panel, we're using the Prefabs folder to store ours. The GameObject's name will turn blue to show that it is a prefab.
We're going to need five prefabs in our game; a wall, a floor,...
