“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 men are without excuse.” (Romans 1:19-20)
Now, if you do believe and you want to choose Jesus’ payment for your sin - so that you don’t have to pay it for yourself with eternal separation - it doesn’t take any real effort on our parts. It was all done by God already. All we have to do is accept it in prayer. All it takes is a genuine desire to turn to God and a prayer that expresses it. There is no magic formula for the prayer, but as I already said, if you “confess with your mouth, ‘Jesus is Lord,’ and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved. . . . ‘Everyone who calls on the name of the Lord will be saved.’” (Romans 10:9-10, 13)
[And here is a secret, you can still choose to believe while having doubts. In fact, we all have various doubts. And exploring those doubts and finding answers and assurances is part of a Christian's journey. But you can still choose to put your faith in Jesus even with doubts. You can still take that first step toward Him.
Or maybe you don't believe yet but you want to believe. Or you want to want to believe. These are good first steps, too. Just tell God about this, what is on your heart. Tell Him you want to believe and that you really want to know if He is real. And then keep your eyes open. And when the desire to give up on Him comes, push past it and keep waiting some more. This kind of "pursuit of God" is sure to awaken all the forces of evil around you, all the forces that want to keep you blind to Him. Give it time and keep your eyes and mind open. God wants to answer these kinds of genuine prayers. But if, deep down, you really don't want to find Him, then you will get exactly what you wanted . . . nothing! So it has to be a genuine desire to find Him!]