An essay is a document based on your view of what you are studying. There are three main parts to it, the Thesis paragraph (opener), body, and conclusion (ending). Each part is important, but the Thesis and Conclusion are what will make or break your essay.
Before you do anything, the writer needs to find a topic in the area they are writing about. It does not matter what the main subject is, you need a topic from it. Someone will tell you what the subject is, that someone could be the instructor, school, or a department Dean. Once that has been done, then look over the subject and find a topic you are comfortable with. Then get it checked with the person that assigned it.
Next step is to develop and write your outline. The outline needs to cover what you are writing about. What each paragraph/group of paragraphs will cover. On short essays a single paragraph for each point of the topic is fine. On larger essays two or more depending on the size are better. Example would be, a 500 word essay would have one paragraph per point of the topic. A 1000 word essay would have two paragraphs per point. A 750 word essay could have a mix of one and two paragraphs, or two paragraphs per point.