Its still just the same as in A5: When you get a black screen after adding a script, there are only two possibilities.

Either your script does not load the level. If you have no level and nothing else, all you have is a black screen.

Or it loads the level, but places the camera in a position where it sees nothing, like in a totally dark room or inside a wall. Then you also see only blackness.

Just look into your script. I advise anyway that you start with the tutorial, for learning some basics of how to work with levels and scripts.