By preface, do you mean an introduction? A preface is generally an introduction to a book, and a paper has no need of a preface, but it certainly has need of an introduction. An introduction to any paper is meant to let the reader know the general subject that is going to be discussed, provide a sense of purpose, give the reader some background information that will help him or her follow along through the paper, and finally, a thesis statement at the end of the paragraph. Let's talk about all four requirements.
For your paper, you might want to get started using the funnel method, beginning with a very general idea and then narrowing down finally to your thesis statement, just as a funnel is wide at the top and narrow at the bottom. You are writing a paragraph for a business class, and your paper is going to be about marketing management. So, you let your reader know this is a paper about marketing, which is a part of business studies. If I were writing a paper on production, for example, I might get my introduction started like this:
There are so many aspects to business, and all are important. But for the company that wants to produce a product, production management is of the highest priority.
This introduces the general subject of the paper to the reader. I have not said anything all that specific, but now the reader knows that this is a going to be a paper about production.
Also notice that I have said that production management is really important, a high priority. This gives my paper a sense of purpose, my purpose in writing and a purpose that will encourage a reader to keep on reading.
What kind of background information might I provide about production? I could mention at least a few ideas, perhaps this way:
Whether a business is producing handmade crafts one by one or producing thousands of a product in a huge factory, the principles of good production are the same. Every successful business must plan ahead to be sure that production is viable, cost-efficient, and profitable.
Then I can move on to my thesis statement, which must state my main idea and the points I will be discussing about that main idea. What is your main idea about marketing management? What central idea have you gained as a result of your project? If I had done a project on production, I might have this as my thesis statement:
In order to have successful production, a business must pay careful attention to location, efficiency, and quality control.
My main idea is that these are the three elements that ensure good production. This statement acts as an outline for me, so now I can develop three sections of my content, one on each topic. The thesis statement also acts as a table of contents for the reader, who now understands what points I will be covering and is able to anticipate them, making reading the paper much easier.
The whole idea behind having an introduction is to let the reader get acquainted gradually with what you want to talk about, provide a little context for the subject, give the reader a sense of purposeful reading, and let the reader know what your main idea is and how you will support it. I hope this will help you get off to a good start!