When you write about a short story, is it true or false that all one has to do is retell the story?
The answer to this question depends upon the nature of the assignment. If you are expected to write a summary of the story, then it is true that you are simply sharing with the reader an overview of the story. But if you are expected to write a literary analysis of the story, that is a very different matter.
In a summary, you will include the setting of the story, its time and place, a description of the characters in the story, and the important aspects of the plot. That is sufficient for a summary.
In a literary analysis, you are expected to find some meaning in the story, some theme, for example, with some literary elements that the writer uses to support that theme, or perhaps an analysis of a character. In a literary analysis, you will want to discuss some aspect of the story that is universal and important.
For example, if I were writing a literary analysis of "Sonny's Blues," by James Baldwin, I might have this as a thesis statement for my analysis:
The darkness of the characters' lives is reflected in the setting and Baldwin's use of imagery throughout the story.
That would be the very last sentence in my introduction. Then I could go on to write two body paragraphs, one on the setting and one on Baldwin's imagery, using details from the story to support my ideas.
It is important that you clarify the nature of your assignment when you write an essay. Whether you are meant to write a summary or an analysis will result in very different approaches.