All stories take place in a fictional world, also known as the diegetic world. The diegetic world is every location shown in the story, and every location implied by the story. Part of good storytelling is establishing where the story takes place. The more the diegetic world resembles the world of the reader, the easier it is to establish the world for the reader.
Once you know the idea behind your story, it’s time to weave that idea into the plot. And one of the more common methods is to create an outline, either before or after writing a rough draft. Outlines help us see the big picture, see how the individual scenes are themselves part of a larger pattern, and it’s often on that larger scale that the idea emerges as the meaning of the story.
Start with a topic, something that interests you. Philosophy can be a great source.