How God exist? I am not sure if this has been asked yet, I just want to know how God came to be from a theist point of view. If not through the creation of humans what would have created God?

To answer your question though, in my opinion gravity creates pressure and attracts other things with gravitational pull, pressure creates heat, heat facilitates reaction, reactions facilitate life and sometimes small to large explosions. ranging form a small crackle or pop to larger ones like the big bang and possibly larger. Things seek balance and there are all sorts of things in nature created to help facilitate the effort toward achieving balance. Balance is unobtainable all life is a mechanism to help facilitate balance. as long as thing remain without balance life should continuously be created. Sort of like a reaction that takes place whenever conditions are right. gravity will continue to pull things together until there is a large enough reaction to counter gravity at which point things will hurtle through space and begin the process all over again. this actually happens all the time even on this planet, be it on a much smaller scale than I am talking about here.

I'm not sure, the big bang sounds like a good idea but I wasn't there so I usually tend to doubt things that I haven't seen with my own eyes. I know, it's not a good way to go through life, but it works for me.

that is the million dollar question that no one will ever be able to answer you. Good luck getting that answer.

We accept things all the time in day to day life that we didn't see. That's what you do when you watch the news, or are a member of a jury or you are programming a computer.

Science is the way we understand the world in order to make medicines and to be able to do surgery. Its how we make cars and electric lights in our homes. To do any of these things people have to look hard at how the world really is, not how they wish it to be. That is very difficult but many people succeed in doing it every day, and that is why we have mobile phones and enough food to feed most of humanity.

For over 150 years we have known quite well about how life came to be, how we came to be. Chemistry allows atoms to form in ways that can make copies of themselves. Copying mistakes and recombination lead to variations. We see that before us in our children. They are copies but they are varied. Over time successive generations are less and less like their ancestors. If a population is separated into isolated groups they vary in ways that make them more different to one another than their ancestors. Given enough generations and they become different species. Humans and Chimpanzees are two such groups that evolved in isolation from a common ancestor group.

The beginning of life, the first life, is less well understood. Scientists work on this by proposing ways that life could have formed in the world as it was 4 billion years ago. They create real experiments and study field evidence to verify or disprove their ideas.

The "Big Bang" is not about the "beginning of all reality". Its about what the evidence shows us about how the universe has changed from a very primitive, simple state over 15 billion years ago to the cosmos we see today. This science is incredibly accurate. How did all of reality begin? We have few plausible ideas and none are yet consider strong candidates. As scientists we don't make up conclusions to fill gaps, we just highlight the gaps and work on filling them in.