Romans 1:20 "For since the creation of the world God's invisible qualities--his eternal power and divine nature--have been clearly seen, being understood from what has been made, so that people are without excuse."
We KNOW God is real by the things He created. If there is a car, there's a car maker. If there is a watch, there's a watch maker. If there's creation, there's a Creator. It is easier to believe that if you put all the parts of a watch in a bag and shake it, that you could pull it out and have it be functional and working, than to believe that there is no God.
Even if there was a Big Bang, who or what created the things that bang? No, God's invisable qualities are clearly seen.