The usual steps (and documents) involved in writing a feature screenplay:

The Premise (1-3 sentences) The Premise (sometimes called the Concept) is a
simple statement of the main character/s, and their dilemma.

The Synopsis (3 paragraphs) The synopsis is about 3 paragraphs long, and
reflects the beginning, middle and end of the story.

The Outline (1-3 pages) One or Three pages, describing the setup, development
and resolution, and sketching the details of the characters.

Character Notes (1-3 pages for each major character) Outlines the different
characters, and their Backstories.

Pitch Document (10 pages) Contains all of the above documents.
Scene Breakdown (2-3 pages) A `beat sheet' or list of points, outlinin
g the key event/s of each scene. Can also be done on approx 60 index cards
(one for each scene).

The Treatment (20-40 pages) Twenty to forty pages, a short story virtually, which
is simply an expanded version of the Outline, but with more
character detail, and various dramatic `moments and key scenes
fleshed out in more detail. Usually each scene is a paragraph.
Contains no direct dialog, and is written in the third-person present
tense.

Sample dialog (1 page for each major character) `Test scenes' or monologues, so
that each of your characters speaks in their own distinctive voice.

The Screenplay (120 pages) 105-120 A4 pages, in standard Screenplay format, in
Courier 12-point font, and with black card front & back, 3 hole
drilled & 2 brads in the top & bottom holes. Has scene headings,
stage directions and dialog.