This sounds as though you are expected to write what some people call an "identity essay." I am not sure for what course you are assigned this project, but you will want to consider that as you think about how to focus your essay. For example, if this assignment is for a sociology course, you would probably focus on how the social groups you are in have helped to forge your identity, family, extended family, ethnic group, religion, and so on. If this assignment is for a psychology course, you might want to focus on both nature and nurture, how your upbringing has helped form you and also how you may very well have brought some genetic material of your own, perhaps shyness or risk-seeking behavior, as well as how your gender affects who you are. If this is meant to be a paper for an education course, you might be writing more about what you bring to the table as a teacher, patience, perhaps, or a sense of humor.
In any of these cases, or for a course I haven't thought of, try thinking about your qualities. You might be introverted or extroverted. You might be someone who thinks things through slowly or someone who feels a need to make quick decisions. You might be a very logical person or function largely on intuition. Are you deeply romantic or practical? Think about what people would say about you if they were writing a paper about you. Think about the activities you enjoy doing and what they might say about who you are. Whom you choose as friends might say something about who you are, too.
To the degree you need to focus on how other people have influenced who you are, make a list, family, community, and friends. You might have a parent who made you a reader, or a sibling who made you love sports. A teacher might have nurtured your debating skills. You may have been raised in a household in which gender-specific activities were emphasized or frowned upon.
Who we are is seldom something that we can state in one sentence. We are usually a collection of qualities, formed by genetics and the world around us, both working together to form a unique person. Having to write this essay will be an inner and outer journey for you, and it is a good way to start thinking about your uniqueness and how you came to be the special person you are!