In the blurred reality of humanity you can be sure of one thing, then surely it is that you exist. Even if the world were a dream or a hallucination, it would still need you to be dreaming or hallucinating it. And if you know nothing else about yourself, surely you know that you have a mind, one perspective on the world, one unified consciousness? Astonishing though this thesis can sound, there is a danger here that we could overstate just what this lack of a unified pearl of self at the heart of us really means. Many writers, such as Blackmore and Metzinger, draw the conclusion that the self is an illusion. This is true in the sense that it is not what it seems to be. But that is not to say that the self doesn't exist. Think if you must of the simple statement made by Descartes; "cogito, ergo sum"
We are the product of random occurance, as this is what evolution is, and why we are here is just as simple. To have children. Our main goal according to biology if you don't add in the whole human elemant, is the goal to pass on our genes; this is another mechanic of evolution and these mechanics are why we really exist. Remember though evolution is just a theory, and who knows we might just be a marble on phone light, but evolution makes the most sense to me, so this to me is why we exist.
There is not an answer worthy of the name. Many people over the ages have tried to answer why god/first cause/the cosmic/ the deity created us. Some have suggested that the deity had something to gain by creating the universe but that's foolish, what could an all-powerful deity gain it didn't already posses? Others have suggested that the deity was lonely but this is false for how could an all-powerful deity be lonely? Still others have suggested that the deity was compelled by an internal nature to create but that would suggest that there is a force outside the deity, that something acted on the deity and how can that be? All that we know is that the physical universe exists, that the deity created it, and that it derives some satisfaction from creating otherwise, why would it create? To ask this question is philosphy, to answer it wholly depends on your metaphysical/religious inclinations. And whatever your answer is your right!
@ianspigler- that is a very deep answer, yet, very true. We were created by an all-powerful, intellectual God. He did not create the world to gain anything, nor because he was lonely. It will forever remain a mystery because our minds are not capable of comprehending such things. We live in a 2 dimentional world, whereas God lives in 3. Therefore, we will never fully understand his ways.