The best way to prepare for this essay is to get to know yourself better to see how you fit into the area of computer science, which is very, very broad, and then talk face to face in person with people who are working in the area that you find to be most suitable and interesting. These people can give helpful input and assistance on introducing you to that career area (to see if it is indeed suitable and comfortable) and possibly giving you ideas to prepare for such an essay. This will give your essay more of a focus, which is very important in your education/career journey.
Getting to know yourself and how your personality traits relate to people involved in various career opportunities is very important in your decision making process. During my many years in Human Resources and College Recruiting, I ran across too many students who had skipped this very important step and ended up in a job situation which for which they were not well suited. Selecting a career area is like buying a pair of shoes. First you have to be properly fitted for the correct size, and then you need to try on and walk in the various shoe options to determine which is fits the best and is most comfortable for you to wear. Following are some important steps which I developed during my career which have been helpful to many .
Ken recommends the following next steps: