This requires a full answer, and you need to go back to when you left school in order to be able to answer it. What were your long-term ambitions at the time? Were there certain subjects you particularly enjoyed at school and wished to continue to study? How and why did you choose your particular course and your specialist subjects?
Perhaps you studied as a mature student. What factors led to your decision to return to learning in this way? The employer will be interested in your motivation. It is important to show that you did not just drift into attending college on the academic conveyor belt but that you made your own clear choices along the way.