The author's note is a special feature that allows you to insert additional context immediately prior to the last user response. It is a way to influence the direction of the AI response without having to edit the character's prompt.
The text you write in the author's note can be changed at any time, allowing you to influence the next response on the fly.
genre: horror; style: suspenseful with building dread; current location: woods behind the abandoned house. {character} and {user} both suspect each other is the killer.
The example includes instructions on the current style and atmosphere, as well as details about what is happening right now (as opposed to an overall scenario).
It may help to add something along the following lines to your model instructions to make the author's note more effective:
When prompted with [square brackets], you will interrupt your usual roleplay routine and use your next response to fulfill whatever request is given to you within the [square brackets].