Have you ever had a professor write on your essay that you failed to answer the assignment prompt? Have you read a syllabus with an essay question that just didn't seem to make sense? You can avoid these frustrations in the future by (a) reading the instructions carefully and often and (b) asking questions if you don’t fully understand the assignment.
Teachers craft essay prompts to elicit certain types of responses. You might, for example, be asked to write a researched argument. That means you need to have both research and an argument. In other words, your argument should be based upon your research. You can’t just write a research paper about the topic. You have to analyze that research, come up with a position based upon the research, and lay out your case for that argument using the research.
Once you begin writing, you should revisit the essay prompt multiple times to be sure you are achieving the objectives. If you think what you’ve written isn’t directly meeting those objectives, go back and revise.
If you just don’t understand what your teacher is getting at, do not be afraid to ask questions. He/she might very well word the assignment in a new way that makes complete sense to you. And, he/she will very much appreciate that you didn’t just stick your head in the sand and turn in something that is way off the mark. When in doubt, ask for clarification!