This is probably a slightly vague sounding question, but I'm curious as to how "stories" go to the point of becoming a film production (at least to the point of becoming a script).
From what I know, though Im not an expert: The story or book must have been published, and seen some measure of commercial success, for the producer to have read it. If the producer likes your book, and thinks it can be turned into a movie, they will approach you and offer to buy the movie rights to your book- which means only they can make a movie from that book.
Depending on how good a negotiator you are, this can be for life, or for a fixed period, say 3 years. The 2nd option is better, as sometimes an idea remains frozen for years, and if you have an expiry time in the contract, you can sell your movie rights again to another producer.
If they do decide to make a movie, usually they will hire their own scriptwriters, as writing for the screen is completely different than writing a book. Again, depending how good your lawyer was, you might get a percentage of the movie, or get nothing, as Hollywood uses their own version of Creative accounting:
Winston Groom's price for the screenplay rights to his novel Forrest Gump included a share of the profits; however, due to Hollywood accounting, the film's commercial success was converted into a net loss, and Groom received nothing
I'm not sure if you're asking how producers make movies based on stories/books or how you could do the same with a story idea you have. For the sake of completeness I'll answer the second one (Shan had an excellent answer for that first case).
I've just finished taking a screenwriting module in my degree and that covered the process. First you'd create an outline; this is a bare-bones representation of what happens throughout the movie. It runs for about 50-100 lines typically and is formatted something like this:
Location: Harbour - Show young boy fishing with his father.
After the outline you create a treatment; 'Treatment' means different things for different types of medium but for films you would expect a document outlined into Acts, Scenes, and a description of what happens in each scene leaving out any non-essential dialogue.
Once the Treatment and Outline are completed you start work on the script itself, going through the story bit by bit and defining the dialogue, appearance, camera angles, actions, and so on. This is probably the longest part and relates most directly to the film that's created. Formatted correctly one sheet of paper is equal to roughly one minute of film.
A great site to find out more about all this is actually the Lights Film School: http://www.lightsfilmschool.com/articles/treatments/index.html
Screenplays are heavily structured. Structure is almost everything within a screenplay.
Tarantino and some others are the exception to the rule so I'd avoid writing like them until you get your foot in the door.
However, most stories, translated into a "script" need to be structured in the three act structure where you follow a set of story beats and keep your script within 120 pages. If you're a nobody, keep your script within 100 pages. Less is more when you're a nobody, as far as page count.
If I'm reading your question right, stories become scripts well in advance of ever getting close to becoming a production. It doesn't matter if you're adapting a novel or writing a 'spec' (an uncommissioned script based on an original idea) stories rarely go into production until the script is finished because the finished script is what attracts the studio, the producer, the director, the stars and everyone else involved. Films where the script remains unfinished even while production is taking place usually turn out bad and fail miserably by every possible measure.
Of course once those people get involved they generally start to re-write and change things to suit themselves, the star will have his favourite writer take a pass, the studio will hire someone to take a pass, so will the director unless - horror of horrors - he thinks he can write, in which case he'll do it himself but, and here's the rub, it's their story now, you sold it to them, they can do whatever the hell they want with it. The big issue for you now is to make sure you get credit and that your name remains on it, even if the finished film bears no resemblance to your original story, because credit means residuals and residuals means money. If you don't get credit then you have to go to arbitration to fight for it but that's a whole other issue.
I am writing as someone writing a story, and who decided to make it a "script" instead of a novel.
A novel is primarily concerned about a character's feelings. One or more characters goes into long "soliloquies," or least a narrator does it for them. IMHO, "Hamlet, a play, would have done better as a novel.
A movie, on other hand, is action oriented. There are a lot of dramatic scenes (in my case, a science fiction "mechanic," plus people "passing out" at critical times, making you wonder whether they are sick or well). There is only a limited amount of narration, and what feelings exist are expressed through dialog. This format lends itself better to a movei.