When you write a text in an academic setting, in many cases you primarily will be providing information, but often you also will be proposing and defending an idea or thesis and offering a conclusion about the topic. These works are not mystery stories; you should tell your readers what conclusions you reached at the beginning of your text, not at the end.
So you must start with a thesis statement, which I define as your conclusion based upon your research. A thesis can be understood to be an assertion;this assertion must be supported by evidence that a reasonable person would accept.
You can think of a thesis statement as being similar in nature to the cases prosecutors present during a trial. During the opening statement to the jury, prosecutors explain crime and the defendant has been accused of committing what laws are involved, then provide an overview of the case they will make to prove their conclusion. In this analogy, the judge and jury are equivalent to the professors or administrators or editors who will read your text, and the prosecutors conclusion is equivalent to your conclusion-based on the results of your research-which you are previewing in your thesis statement.