How do i sell a story i wrote?

I would try and find a literary agent through Google and submit your story to them. Normally it would either be a novel which the film rights are then bought to. A screenwriter would then adapt it for a movie. Im not sure if you mean you have written a screenplay or novel. Get professional advice would be the first thing that i would do. If you have no luck try associated content or similar sites.

This is a small idea.... send a part of your story,just as the theme line and stop the story where u can attract people to read more then will ask for the whole story.Then u can manage urself.

You definately need a Literary agent who specializes in what you are looking for. Most of the larger publishing houses won't even look at unsolicited manuscripts. In other words, they won't even look at your work unless you are represented or you query them and manage to actually get them to take a look at your work. Absolutewrite.com offers a list of agents to beware of and they have tons and tons of information in their forums for writers.