“Why do humans exists?”
God created us.
Thank you, and enjoy your day.
Philosophers have debated this subject for centuries and all that they can conclude is that we think and so we exist.
We really don't understand consciousness and the problem is that we are constrained by our senses. The real world looks nothing like what our senses tell us. Our senses are only a construct to help us survive and procreate.
If the brain is an organ that simply processes sensory information from our senses and stores that information in memories, then what drives the brain to create new ideas that didn't exist before and string those ideas together into a very complex and abstract models that explain how nature behaves through the scientific process.