This is a question that has plagued many a young teenager and even someone in their adult life. Ask youself: what are my strong points? What are the qualities people admire in me? I have asked the same question as you, quite a while ago in my young life and I found that, when I looked deep within myself and found the positives within me, I had a lot to offer this world. We all get down on ourselves, but instead of looking at everything that's wrong with us, start looking at everything that's right with us. Once you see your value and your worth, you will be amazed at what you can achieve. My biggest purpose in my life is my son, a blessing from God. All the best, and I hope you find your purpose soon.