Even if you don't begin with a story, you must end with one, and it must be a real story, one that fascinates and excites readers and is fully satisfactory to you. That's the job.
Since any plot will consist of the storytelling methods that organize narrative energy and drive it forward, plot is often described with metaphors of machinery: We speak of plot “mechanisms.” They are nothing if not concrete.
Like that dream, your story has to be unearthed in the depths of your imagination.
“I invariably have the illusion that the whole play of a story, its start and middle and finish, occur in my mind simultaneously—that I am seeing it in one flash. But in the working-out, the writing-out, infinite surprises happen. Thank God, because the surprise, the twist, the phrase that comes at the right moment out of nowhere, is the unexpected dividend, that joyful little push that keeps a writer going.”