Some questions are often not so simple as they seem. Just like TELL ME ABOUT YOURSELF.
Start by defining what you do as it relates to the job, think about few past experiences that are relevant to the job and try to quantify in terms of time, money or people. Then list the strengths you have that are pertinent to this job (experiences, traits, skills, etc.). All of this adds up to the message you want the interviewer to know about you when you leave.
It is also done to test your knowledge and creativity of presenting yourself. This is the question that makes almost everyone nervous, so prepare yourself well before the final day to be more confident and relaxed. Practice is all that makes things perfect. Do not just sit and wait for the things to happen. Take control beforehand and do not let this opportunity slip away.