A screenplay is just a format. I grew up with a screenwriter (failed) for a step-dad, and I've written a few short stage plays myself.
You basically just have to set up every scene individually. You have to set up the scene (describe camera angles, zoom, pan, fade to/from black etc.),
Describe the scene (Objects and characters, highlighted by ALL CAPS, so crew can look at the script and know what props need to be in the scene...).
Follow dialogue format (Every dialogue is separated by a double space, with character speaking in bold and all caps followed with a colon, simple
stuff).
Here's a small one that I wrote about Drunk warning a number of us
about short posting
And then just be creative. I want to write a screenplay soon, too.
No need to worry about the formatting now, though. Just sketch out your dialogues, and describe in concise terms the scenes. Piece it together and
polish it later!
Good luck, man!
DeltaChaos