A beat sheet is a writing tool used by film industry writers, directors, and producers to identify in broad strokes the sequence of events, and actions in a story. It is an abbreviated way to break down the structure of your story, making it easier to organize and change.
The beat sheet charts the sequence of events that cause your main character to do something and maps how your main character progresses in his change from the beginning to the end of your story.
Create a beat sheet by using bullet points that illustrate in one or two lines the order of your plot’s progression. Remember plot takes place when a character does something or acts upon another character.
A beat sheet is a diagnostic tool, not an end in itself. There are no hard and fast rules—it’s like jotting down the main turns on the map that takes you to the end of your story.
Then you let a road guide take a look at it, to make sure it’s going efficiently where it is meant to go.
When you actually drive there, you’ll know where you’re going—and you’ll know that your creative time not only knows but has helped you make the best possible route.
--From KJA’s notes to Writing Treatments That Sell.
For someone that is new to the business of writing screenplays, the term "treatment" will most definitely be new to them as well. Basically, if a writer has an idea for a story but for one reason or another does not want to write an entire script, they'll need to know about treatments.
Click on book to Amazon for your copy of Writing Treatments that Sell on Amazon.