Look up some script formatting, first, to get the basis on how a script should be outlined. There are plenty of sites out there.
Second, READ READ READ. The more you read screenplays, the better because you will be influenced by different writing styles, which in turn will help you critique your own, and better develop you as an artist.
My suggestion to you is to write out a treatment of your vision. Look up the rules for writing a treatment. You want it to be in third person, and basically describe what it is you will see on the screen. Leave out character emotions (this goes for screenplays as well.) For example, you cant write "He was nervous," because the audience won't get that. Writing for screen is a visual style of writing, as opposed to prose. You would write something along the lines of "His fingers tapped the leg of his jeans, with a rhythm that became more and more sporadic, like the thumping of a drum. He licked his lips intensely, while his eyes shifted left and right, finally coming to rest in a deepened gaze upon the ground." etc, etc.
After you have a treatment (again, research the way to write one), then proceed to write the screenplay. Honestly, my approach for starting out would be to take it a step at a time. Even before writing a treatment, you should lay out a three-act structure, and label each plot point (inciting action #1, Climax, empowerment), as well as outlining the key points: Exposition, Rising Action, Falling Action, Resolution. This is your template for how your story will develop.
Then, write your script scene-by-scene in linear fashion (my suggestion). After which, you can then go back when revising and begin playing around with the order in which the scenes appear. OR make a more detailed act-structure and maneuver incidents around on that before writing the script.
Take a look at some earlier Christopher Nolan movies. He is notorious for his non-linear story telling (ex: Memento).
The crucial thing becomes research. Research other writers work, research how to make and refine your plot and characters so that it has depth and good emotion, and research how to write a script. From there it becomes a game of seeing what you can add, and remove, that lends more drama or suspense (even for comedy) that will keep the audience locked in.
