For my keybording class I have to write a short story. Everyone is writing a comedy but I want to write a horror. I've always had trouble with writing stories. It's not English class and I don't have to follow any kind of format. The only directions we were given was type an appropriate short story that's at least 4 pages.

These are some of the thing I'm stuck
on:
I have no idea how to start it.
I don't know what point of view I should write from
I don't know how to add dialogue into the story
I don't know how to add a twist

If it helps these are the ideas I have:
A young couple with a little kid or a baby. They hear stuff over the baby monitor like the kid talking to someone. The kid claims that he was talking to his imaginary friend. Maybe at some point the mom hears something like a strange voice or the fathers voice but then he walks in the room. Maybe they will find out someone died in the house or they will find someone in the kids room. Maybe the couple had dead baby or something

Some story were the twist is that the main character is actually the killer