Help! Simulator device screen is black

Hi! I just built my very first tiny game in Xcode using only buttons and labels (I followed a choose your own adventure game youtube tutorial), and when I go to run it, it says the build was successful, but the device simulators (all of them) have a black screen when I try to run it (although the desktop screen looks normal). Same thing happens when I connect my iPhone to run it there.

I have never written a line of code in my life, know almost nothing about computers and nothing about programming, and I was really proud of myself for getting this far (especially since I had to navigate problems and differences between the instructor's version of Xcode and my version, which is 10), but now I can't run my game! Can anyone help me figure out where I went wrong? And please explain it like to a 5-year-old. Thanks!