Essays are arguments presented in a logical linear order. It is a presentation of ideas, one at a time, in a logical sequence that the reader will understand. However, your essay structure will reflect your claims and, thus, may need a different structure than the classic structures.
Essays include different parts within them: introduction to the argument, analysis of data, presenting counterarguments, and drawing a conclusion. It could also include the context of your argument, a summary of relevant information or the definition of important terms. While the introduction is first and the conclusion is last, the parts in the middle must be structured in whatever way presents your argument best.
One way to structure the body of your essay is to answer reader questions in a logical order: What – evidence shows that your thesis is true?; how – does your argument do against a counterargument; and why – why does this matter to anyone but the author. You need to think about what your readers will need and where to put the parts of your argument in order to facilitate your readers’ understanding.
Please check out this site for ideas on mapping your essay structure: http://writingcenter.fas.harvard.edu/pages/essay-structure
For a basic essay structure: what is in the introduction, the body and the conclusion, see http://www.library.dmu.ac.uk/Support/Heat/index.php?page=482 at De Montfort University