Stories are written like a script, one line at a time. Pick what the next line is: a Scene heading (where and when, like INT. NIGHT BUS - LATE), Action (what happens), or one of your characters to give them a line. Press Enter or Add Line to add it.
Tap any line to change it, move it or delete it. Scene Break adds a pause between scenes, and Preview shows your story the way readers will see it.