Being an aspiring writer myself, I've learned that in order to get the attention of potential suitors you need to be able to provide a good synopsis/log line.
It all depends on your style of writing. Perhaps you like to just get right down to work and type out your story straight into the screenplay software, or like me you like to outline and make endless notes before actually writing.
Or others who still like to write it out on a pad of paper. No matter what style you write you have to be able to sum up your story in a short item to present to production companies, agents, managers etc. if you want to spark an interest. It has to be short and punchy. Remember these people read hundreds, if not thousands of stories every year. They've seen it all.
This link from Screenwriting Spark has some great resources to help you shave down your ideas.
They say it's easier to cut away than add, but what you will find is that when you think you've cut away a lot of the fat, there is still a lot more to cut. Trust me!
Hurry up and Wait Link: http://goo.gl/fGWTcO