"Plot" is a literary term referring to the central action in a work of literature. If you need to summarize a plot for a homework assignment, you should focus on events that move the story from its initial conflict to a climax and resolution rather than examining such details as the setting or the psychological or social elements of the story, except in so far as they contribute directly to the main action.
Most stories have a plot that begins with a "protagonist" or central character encountering some sort of problem or conflict. Sometimes the problem is an external conflict with another character or "antagonist" while other times the conflict is an internal one, involving ethics or making decisions about what sort of life the character wants to live. Normally a plot revolves around how a protagonist resolves the central conflict of the story. In a romantic story this might involve two lovers overcoming obstacles to getting married while in a mystery a detective might identify a murderer.