I understand that many people don't believe in God; or that Jesus is his only son; or that the Bible is God's inspired word. We can't truly believe until we have seen or experienced God. Why have we not seen God - because we have not looked. God said he left evidence for himself everywhere we look, and he promised he will reveal himself to those that earnestly seek him out--God cannot and does not break his promises. There's plenty of evidence to be convinced there is a creator - more than enough to cause us to want to know more about him. My favorite place to suggest where people might see evidence of God is to have them truly ponder the artwork of God in the animal world - can anyone truly imagine the designs, patterns and brilliant colors of nature simply evolved through random chance of how the DNA happened to line up? To dismiss these works of art, is to dismiss God.
Assuming God exists, I think everyone would agree he could convince the entire world of his existence in an instant if he desired to do so...(actually, one day he will, but then it will be too late to make a decision). God made the universe, and makes the rules, and has told us he will reveal himself to those that seek to know him. One way to look at why he might have decided this is to consider that if God did the supernatural events that would force us to accept him, he would be forcing people to want to be with him. That is not his plan nor his intention. Consider, if we were to seek our spouses in that way -to make who we desired love us we might drag them off to a cave and make them live with us - or else! Or we could threaten them enough to force them to "love" us. That would be unthinkable to us - why would we assume a perfect God would force us to love him?
But maybe you don't reject God, but do reject Jesus?
But what if you don't reject God, but don't believe Jesus is his only son who he sent to save the world? Instead of learning about God's plan, you lived your life largely ignoring God and taking advantage of all the great stuff he provided for us. So imagine the end comes in one form or another, and you are all of a sudden standing before Jesus...he asks "Why didn't you seek to know God?". Your answer is likely some form of "I was not concerned enough, or did not care enough about you to bother to look" - "I was busy with my own desires" - not much of an excuse. Not that any excuse will work - we made our decision for whatever reason and it will then be too late to change. The consequences of such a decision are unthinkable - we have been warned.
How do find out about God?
God says over and over again in the Bible that we will only find him if we seek him with all our heart. That does not mean we need to believe in him to find him - but just that our hearts need to have enough desire to seek to learn about him. This assumes you have looked around the earth and concluded there must be a creator - a God that made everything. Your honest search will not come up lacking - God promises, "If you seek him, he will let you find him".
Verses about this promise of God...
Deu 4:29 "...you will find Him if you search for Him with all your heart and all your soul.
1Chr 28:9 "...the LORD searches all hearts, and understands every intent of the thoughts. If you seek Him, He will let you find Him; but if you forsake Him, He will reject you forever.
2Chr 15:2 ...the LORD is with you when you are with Him. And if you seek Him, He will let you find Him; but if you forsake Him, He will forsake you.
2Chr 15:4 "But in their distress they turned to the LORD God of Israel, and they sought Him, and He let them find Him.
2Chr 15:15 ...they had sworn with their whole heart and had sought Him earnestly, and He let them find Him...
Prov 8:17 "I love those who love me; And those who diligently seek me will find me.
Jer 29:13 'You will seek Me and find Me when you search for Me with all your heart.
Jer 29:14 'I will be found by you,' declares the LORD...'
John 1:45 Philip found Nathanael and said to him, "We have found Him...Jesus of Nazareth, the son of Joseph." (notice, Jesus did not find them, they found him)
Some other verses to ponder...there is still time...
1Cor 2:14 But a natural man does not accept the things of the Spirit of God, for they are foolishness to him; and he cannot understand them, because they are spiritually appraised.
2The 2:11 ...For this reason God will send upon them a deluding influence so that they will believe what is false,
Heb 11:6 And without faith it is impossible to please Him, for he who comes to God must believe that He is and that He is a rewarder of those who seek Him.
I don't think it is so unusual to doubt all these things, so that's not really a problem - we all have had serious doubts at some time. The problem is not in doubting, but in not caring enough to find out what the truth is.