Stu Maschwitz offers an overview of outlining in Fountain:

Organization and structure are such an important issues that I made sure Fountain had some provision for supporting them. Fountain’s Sections are invisible, hierarchical markers that you can use to demarcate the structural points of your story—or anything else you like. Synopses allow you to annotate a Section — or a Scene Heading — with non-printing descriptive text.

You can add Sections and Synopses to your Fountain screenplay as you work, or as a part of rewriting. You can also begin the writing process with them. You can use them to denote scenes, sequences, act breaks, or whatever is helpful to your writing process.

Because they don’t print in the formatted script, section and synopsis tags can help you structure the document in a way that makes sense for you as you’re writing. Rather than just a scene header like…

EXT. BEACH – DAY

…you can throw a meaningful label on it like…

##Giant crabs attack campers

EXT. BEACH – DAY

When we were drafting up the Fountain spec, I honestly didn’t pay much attention to these tags, because I didn’t think I’d use either much. But in writing my ABC pilot, I found them genuinely useful.

I used the top-level section mark (#) to denote act breaks, and the synopsis tag (=) to quickly jot out what was happening in upcoming scenes. That’s great for the end of the day, when you’re leaving some gas in the tank for tomorrow’s writing.

The = can also serve as a quick-and-dirty to-do list, such as:

INT. BEDROOM – DAY

= shorter. start on Asha

Several of the existing Fountain apps — and many of the upcoming ones — can do magic things with section and synopsis tags, formatting them differently or collecting them for an outline view. Together, they make it easier to jump through your script. Rather than looking for a page number or a location, you can skip right to the section or note you want.