How to begin Writing a Story or Script?

I am in a similiar situation. I have an idea for my story or at least the germ of an idea, but I don't know how to begin writting about it. I was starring at my blank computer screen for awhile but found that intemidating so I wrote out the idea at the top. It didn't really help. How do you get that first sentence out on paper. I've never really gotten stuck at the begining like this before and I'm not sure what to do.

A short story is in some ways more difficult to write than a full-length book. Your short story should have all of the plot, characterization and meaning of a book, but written in only a few pages rather than a few hundred. A short story has fewer characters than a full-length novel, and covers a shorter span of time. Usually these stories cover only one event and focus most of the story on only one character. Short stories vary in length, but are generally shorter than 7,000 words. Make every sentence count. Because of the short nature of the story, every sentence you use should convey information. There is no room for filler or a lot of secondary characters. Each sentence should fill in the setting, flesh out the characters and further the plot. Limit the numbers of characters that you introduce. In a short story format, there are only so many characters that a reader can get to know in the course of the story. The number of characters should be kept to the minimum number necessary to tell your story. Start the plot right away. With a short story, there is no time for gradually setting the place and time and introducing characters slowly. The plot should begin with the first sentence, starting in medias res if necessary. Use dialogue to further the plot. In a short story, there is not enough room for rambling dialogue or a lot of conversational small talk. The dialogue should be pushing the story forward. Limit the time period of the story's action. The action in most short stories encompasses a short time period, such as a few weeks, one day, or even less. Though an interesting idea, an epic tale scattered over a century will almost certainly not work well in a short story format. Concentrate on the details. Because there is not time for lengthy descriptions of the setting and characters, the details present in the story can go a long way toward revealing both. If there are no wasted words, there will be enough room to provide effective characterizations and a setting that the reader will be able to picture easily. Make an outline before starting. With a lot to be accomplished in so short a space, it may take some working and reworking to get it all in there. An outline can help you to remember which plot points and characters you want to include in the story. Once you have an outline, it is a matter of building on it to create a fleshed out story that makes an impact. In today’s busy world, there are many readers out there who simply don’t have time to read a lot of full length novels, and short stories are a great way for busy people to get their fix of fiction stories. Short stories also open up different publishing markets that are not available to full-length books, such as the many magazines that publish short stories.

Read as much books as you can. Especially interesting novels of well-known successful authors and scriptwriters. In that way, you can have an idea of their ways of making stories and scripts.