You write essays in school exams based on the teacher's specific question to show what you have learned. The question becomes the introduction section. You then proceed with a linear description of the history surrounding the question. The last section is a conclusion to the history, how it ended, or what the solution was. The map here would be Introduction, Timeline in Events, then the Final Conclusion. For example, you may be asked to write an essay on Vincent Van Gogh as a unique painter.
Your introduction states what your essay will be about; you can accomplish this in one to two opening sentences. Giving a little background to the subject is also helpful to provide a better idea of the subject matter. For example, the essay question could be "Why was Vincent Van Gogh considered such a unique painter?" Start out with background on Van Gogh and lead into the question as part of the introduction.
Start writing down aspects of Van Gogh's painting that are unique to his styles such as uses of brush strokes, lighting aspects and subject matter. Each is a supporting statement or argument to the piece as part of the essay map. For example, no one else used brush strokes like he did. You can look at any of his paintings and know right away who painted it, just by the brush strokes alone.
Another argument, or statement to support Van Gogh as a unique painter, would be the use of light and the subject matter of most of his paintings. Most of his paintings used scenes from the countryside in which he lived. He used vibrant yellow and orange tones to reflect the sunlight he saw in the fields. Then make your conclusion, based on the evidence you have given in the essay. Your essay map for this example essay is Introduction or Statement, Argument 1, Argument 2 and the Conclusion.