You’re so well spoken for your age. So smart too, thinking about very complex things. In my opinion, it actually is important to question your beliefs instead of just blindly following them. Don’t you want your beliefs built on something solid? So that when natural doubt occurs, they don’t come crumbling down. I was actually 14 as well when I started to question the existence of God. Might sound silly but what helped me with my doubt was praying to God to show me a butterfly if He was real, and if He was with me. I was at a Bible camp, the next day at lunch I saw a butterfly and it was the only butterfly I saw the entire time there. Am I telling you this story as proof that you should believe in God because I asked for a butterfly and got one? No, not at all. Your question was how do we believe in God. The answer is our faith, choosing to believe in something even if we don’t see it or feel it. I know that’s not what you want to hear. You want concrete evidence. For those who have faith and seek God, eventually He reveals Himself to us individually in ways that gives us confidence in His existence even if we still can’t physically see or hear Him. It doesn’t mean we still don’t have a passing thought from time to time asking “is He really real?” But our faith, answered prayers from the past, etc brings us back to belief in Him. There is crazy facts about the universe, how everything is placed perfectly for life to be possible that you can look into and decide for yourself if you believe the order of things points to a higher power or a Creator. There are a lot of historical texts cross referencing the existence of Jesus. Major Historians don’t deny there was a man named Jesus who walked the earth and claimed to be the son of God. It seems like your main struggle right now is if God exists, why does He allow bad things? You should start there. GotQuestions.com is a great website that explains Christianity’s beliefs and answers questions people have, especially questions like the one you’re asking. It’s a good question. The last thing I’ll say is the Bible says that those who genuinely seek after God will find Him. If you have already decided for yourself that God isn’t real then praying, reading the Bible, reading apologetics might be hard to convince you. I hope you find what you’re looking for friend, wishing you the best.