"select a company, service or product to market". Plans will be in-depth studies of how to market the company, service, or product you have chosen.
What kind of company can I choose?
I agree with the various suggestions in all of the above posts. In addition, you may want to consider choosing a company that's outside of the typical paradigm of what other students may be choosing. Take a look, through some online research, at the many innovative, creative, and progressive enterprises that are tackling new ways of dealing with old problems. For example, there are entities working with algae as a renewable energy source - producing oils. Many food manufacturers are using cutting-edge processes to produce quality products that make there way to your grocery store's shelves. Again, as stated in the previous posts, pick a company that intrigues you with their products and services and corporate philosophy. The more you are interested in their way of doing things and in what they offer, the more motivated you will be to come up with an equally innovative marketing plan.
I agree with the previous posts that you need to choose a product you know something about. I also suggest choosing one that has a relatively small market. This will make it much easier for you to make a plan. Let's say the target market is students. Since you are one, you know how they think. An example of a product mostly geared toward students would be a personal recorder. Your marketing plan could address how it can be used to record lectures.
It is, as the previous post says, good to pick something that is of interest to you. However, in this sort of thing, it is also important to pick something that will be feasible. One part of your selection process should include thinking about how or whether you will be able to gather the information that you need. It may not always be easy to get information that you might want from a firm.
You might also want to look at your textbook and see what sorts of criteria it gives for how to market a product. Having done that, you might want to think about what sorts of firms would fit with any given template of how to market something that your text provides. These things will make it easier for you to do your assignment.
When you have an assignment like this, it is often best to choose a product or service that you have some familiarity with or that you want to learn more about and that you are enthusiastic about. I do not think you can really "market" a company per se, without marketing whatever it has to offer. If you have a great familiarity with technology and enjoy using it, a technological product or service might be a good idea, for example, the iPad, the iPhone, Google, or Facebook. Sometimes I suggest to my students a marketing plan for their school, which offers a service they are already using. If you are someone who enjoys reading, perhaps the marketing of books would be enjoyable to you. Also, if you have a vision of opening up your own business someday, what service or product would you be selling? You can get a jump start on that business right now, by working on your own marketing plan.