You've gotten some good advice here. And good for you to realize your dream of being a writer. I'd suggest you find a good writers' organization. If you know others who write horror, maybe you can form a critique group and critique each other's work. I write romance and belong to Romance Writers of America and also have a critique group. Perhaps there is a group out there for horror writers. Keep at it. Write your first draft, put it aside for a few weeks (Stephen King says put it aside 6 weeks), then read it all over again and revise. Stephen King has a great book called. "On Writing." I suggest you read that and read other books on writing, such as from Dwight Swain and Kirt Hickman. It is very difficult to find an agent or a publisher nowadays. There was a time when publishers looked down on self-pubbed books, but they don't so much any more. If you self-publish and do promo and your sales are good, a publisher will be interested in your work. Don't give up.