An author/writer is someone who brings ideas that become the moral premise of the story, the form can be anything: ideological conflict, interpersonal conflict, interpretation of human values, or even something entertaining and funny.
But it is not just an idea that lingers in the mind, to be an author, she/he must be able to translate/narrate those ideas into a fictional story usually taking the point of view of a certain character (protagonist) as the center of the narrative.
So that readers can usually capture the author's ideas and even get lost in the author's imagination through the struggles of the protagonist.
So in short, the author is the carrier of creative ideas and narrates them into fiction to the readers.