What is Philosophy?
Nobody really knows. Thousands of different definitions have been given since Western Philosophy began in ancient Greece, but the contents of philosophy over the centuries has been mainly determined by what those people calling themselves philosophers have talked about. And philosophical conversation has covered a vast variety of topics, from science and mathematics to ethics and aesthetics.
Still, philosophy has had some constant core concerns and preoccupations. I would describe the central concerns of philosophy, admittedly vaguely, as the attempt to understand the fundamental nature of reality and the place of human life within it. So the core problems of philosophy include freewill and determinism, the nature of consciousness, the scope and limits of human knowledge, whether there is in reality any such things as moral goodness and moral evil, and any similar puzzle to do with developing a rational and coherent understanding of the world we live in, and how we should live in it.