What am I

You're a human being, which is a species of ape, etc. Look close enough and you're made of atoms, the same as everything else.

What is the meaning of life?

The notion of meaning is a human psychological concept. Whether you see your life as having meaning or not is about the stuff going on inside your head.

Why do I exist?

Because your parents reproduced.

What guides my morals?

Your brain, which is heavily influenced by what you perceive as societal norms.

What are my core beliefs? why?

That's a question of how the brain works, and I don't think anyone really understands it at nearly that level. Also it probably doesn't work like that anyway. The little bit of cognitive science I've seen suggests we really don't have core beliefs, we more do things and then rationalize them.