Setting and At Rise Description Element
Typically, the At Rise and Setting Description are left indented at approximately 3.25" (a little more than half across the page,) running to the right margin.
The Rules: When your play, or any new scene or act, begins, the reader wants to know the Setting and who and what is seen on stage. This At Rise Description is so named because it refers to the raising of the curtain most theaters used to have. While these days curtains are mostly reserved for large, proscenium houses, such as on Broadway, we still need to know what the stage looks like when the lights come up. Older formats would often call for the Setting and the At Rise Description to be separated, but these days we tend to put them together.
At RISE: (A kitchen/living room somewhere in California. Early evening. MARGE, thirty something mother, stops to scrutinize the carton before pouring milk into a bowl of flour. On the table are four place settings, one of which includes a martini.)
From the above description, your reader knows the setting (place and time) of the play, as well as who and what occupies the space when the play begins.
Use the At Rise margins each time a new scene or new act begins. Since the whole idea of starting a new scene is that either the place or time has changed - otherwise, you'd still be in the same scene - it's common sense to set the new scene for your reader with an At Rise description.
How to Describe the Setting
The amount of information playwrights include to set the scene varies incredibly. Here are a few examples:
(A deserted road on the outskirts of a not quite apocalyptic suburbia. Not quite five o'clock in the not so distant future. COWGIRL, late twenties and the Bonnie half of a Bonnie and Clyde team, holds a syringe. Her hands shake. COWBOY, about her age, holds a backpack.)
In Beef Junkies above, I give a sense of the world of the play and the time of day, but "a deserted road" is as specific as I get about the set. But in the opening of The Wash, I give more detail.
(The laundry room of a New York apartment building. Friday night, around nine o'clock. A row of washing machines right. Opposite them, a row of dryers. Center, several chairs for those who wait. JUDITH, mid-twenties, puts her laundry in a washing machine. Her pocketbook is atop Agatha Christie's Dead Man's Folly inside her empty laundry basket.)