The question can be considered from many angles- how did you come to be here, what is your purpose here? Even "here" is relative and could refer to existence in general, or specifically why you are at your station in life, or why you've come to this website.
How did you come to be here? Through a very long and complex chain of processes that have resulted in multi-celled, sentient organisms. A little more specifically, human ancestry can be traced back to South Africa. Hundreds of thousands of years of tool use and expansion have created humans as we are today. Your existence, wherever you are in the world, is the result of thousands of years of migration and adaptation by Homo sapiens populations.
Why are you at your station in life? Whether you are young or old, wealthy or poor, healthy or ill, in school or work, all are dependent upon your cultural history. Hundreds, sometimes thousands, of years of cultural development and change set the stage for your particular class status, ethnic identity, health status, and preoccupations in life.
Why have you come to this website? Presumably for help with assignments of some kind.
What is your purpose in life? This question is hardest to answer. I have attached a diagram based on traditional Japanese philosophy of what different life motivations can be. Depending on what your religious beliefs may be, you may believe that a higher power has determined a purpose in life for you, and it is your duty to figure it out. If this is the case, I recommend building a stronger relationship with the higher power and following their guidance. If you do not believe in such a predetermined destiny, perhaps you could work with the diagram I've shared and make a list of things you like to do, things you are good at, and so on. It could be helpful to ask people around you what they feel your purpose in life may be, as they have different perspectives from your own.
I sense that this question comes from a place of dissatisfaction with your being "here," or perhaps you are a very philosophical person and were seeking a second opinion. Either way, I would like to recommend the website Seven Cups of Tea- it is a free, online counseling service.