Writing the Action
The action part of the screenplay comes after the setting is given.
This writing, sometimes called the narrative, should not be long like a novel or else readers in Hollywood will not take the time to read it. They'll go for just the dialogue and if they don't like it, your script will go to the bottom of the pile -- or probably worse.
Action is what can be seen on screen. It does not include a subjective opinion coming from the mind of the writer.
Here's an example of what to avoid when writing action (italics):
(INT. means an inside)
INT. BEDROOM - DAY
Johnnie looks like he had a hard night. He MOANS. It's almost as if he broke up with his girlfriend. The bed is surrounded with BOTTLES and PIZZA BOXES. It looks like someone had a party.
This is improved below:
INT. BEDROOM - DAY
Johnnie MOANS as he throws the sheets off. He wipes his eyes and rises from the bed with poor balance. His bare feet step on PIZZA BOXES and BOTTLES and he hits the floor with a THUD!
The party is over.
Keep the action short.
Now let's get into writing of the dialogue.