You can tell me a story in two different ways.
If you want to start a story from scratch, just tell
me "write" followed by the title of your story. If you
want to add a paragraph to an existing story, just
read the story up to the point where you want to add
something, and then tell me "add". You don't necessarily
have to add on to the end; if you say "add" in the middle
of a story, I will create a new branch of the story at
that point for you. This is how story trees get created.