The first paragraph of your essay is referred to as the thesis statement. In the opening paragraph, you should provide any relevant background information about the topic, explain why the topic is important and then summarize the argument in a clear, concise fashion. The aim of this opening paragraph is essentially to introduce the topic and briefly explain your argument regarding it. Some students find it easier to write this paragraph after completing the body of the essay, but if you have clearly planned your assignment, you should be able to do this first.
The body of the essay contains a full explanation of the argument, displays points that support your thesis and, ideally, also includes points which do not wholly support it. Transitions are important within the entire essay, but specifically within the main body of the work. Each paragraph should contain one point, an explanation of what is meant by that point and an example of the point in a study or text. These points should all be shown to relate to your thesis, and they should connect to each other logically. The points listed in the main body of the essay should build on one another to create a full picture of your argument. It is also important to include some contradictory evidence. Although you are presenting an argument, it is unreasonable to only include evidence that supports your thesis because it makes your argument seem biased and even poorly researched.
Summarize the argument presented in the body of the essay within the conclusion, and explain how it supports your thesis. Writing a concise run-through of the points you have made may seem difficult, but is important to remember that you are only re-stating information already provided. Anybody who is reading your conclusion has most likely read your entire essay and will understand all the ideas without any additional explanation (assuming everything has been explained clearly in the body and introduction). Re-state your thesis, and discuss the implications of your research and any additional research that could be performed in the area.
"What, Why and How" and "The Five-Paragraph Essay" are two alternative methods for writing an essay that correspond clearly with the basic, three-step method. "What, Why and How" essays begin with an introductory paragraph including a thesis statement, and then move onto the "What" portion of the essay. This explains the research that leads you to believe that your thesis is true, and doesn't include any detracting opinion. The "How" portion of the essay discusses how your thesis applies to different situations, and how it stands up to critique. The "Why" portion is designed to explain why the topic of your essay is relevant to the reader and the world at large. "The Five-Paragraph Essay" simply uses the three parts of an essay as described above and imposes a paragraph limitation on them. The introductory paragraph with the thesis takes up one paragraph, the body of the essay makes up three and the conclusion is a final paragraph. These methods all essentially require you to explain your argument briefly, then go into more detail, providing evidence along the way, and finally to summarize and explain the implications of your argument.