Film Unfriended / unknown user Explanation?

I just watched the movie Unfriended / Unknown User. But somehow I don't understand him. So why, for example. Everyone suddenly killed themselves in a cruel way. And e.g. What that ended up being when someone closed the main character's laptop. Actually, I didn't think the film was a "fantasy horror film". I thought rather "real", something that can really happen. But that a dead girl writes to you and that you all suddenly kill yourself in a really CRUELY way and still end where someone (I think the "ghost" of Laura) closed the laptop.

So can someone explain this film to me?

Laura took her own life for bullying, but her spirit lives on.

I assume that the clique during the video chat all participated in the bullying at the time. Laura kills everyone one by one.