Assume that I am a layman without knowledge other than science-related ones. How should I do to be a Christian in a correct way?
In more strict words, what are the "correct" steps or algorithm to be a Christian? In more honest words, is assuming God(s) exist(s) the first step? You can also think of how do you persuade me to fear God, etc, etc.
I hope this question will be reopen to let others help me go to the heaven!
Yes, belief in God's existence is the first step. As Hebrews 11:6 says,
And without faith it is impossible to please him, for whoever would draw near to God must believe that he exists and that he rewards those who seek him
Beyond that, the good news of the Gospel is that Jesus already has taken the first steps toward you becoming a Christian.
God is love. Whoever lives in love lives in God, and God in him. 17 In this way, love is made complete among us so that we will have confidence on the day of judgment, because in this world we are like him ... We love because he first loved us. 1 John 4:16-20
While the exact process of "conversion" is a matter of some debate, the sign that it has occurred is not - you are to grow in Christ, bearing fruit in keeping with repentance. As Paul says,
But the Holy Spirit produces this kind of fruit in our lives: love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, and self-control. There is no law against these things! Those who belong to Christ Jesus have nailed the passions and desires of their sinful nature to his cross and crucified them there Galatians 5:24
Just remember, we obey out of love, not out of a need for love. As Jesus said,
If you love me, you will obey what I command John 14:15
This is the way of the Gospel- that God loves us, and we in turn respond in obedience out of love,
For it is by grace you have been saved, through faith—and this not from yourselves, it is the gift of God— not by works, so that no one can boast. Ephesians 2:8-9
Or, if you prefer it all one text, consider Titus 3:3-8
At one time we too were foolish, disobedient, deceived and enslaved by all kinds of passions and pleasures. We lived in malice and envy, being hated and hating one another. But when the kindness and love of God our Savior appeared, he saved us, not because of righteous things we had done, but because of his mercy. He saved us through the washing of rebirth and renewal by the Holy Spirit, whom he poured out on us generously through Jesus Christ our Savior, so that, having been justified by his grace, we might become heirs having the hope of eternal life. This is a trustworthy saying. And I want you to stress these things, so that those who have trusted in God may be careful to devote themselves to doing what is good. These things are excellent and profitable for everyone.
Every person's journey to God is different. God understands that, and is capable of revealing himself, drawing you to him, in a way that is specific and meaningful for you. He actively wants to do this, and your job is to cooperate if you wish.
You describe yourself as "a person without knowledge other than scientific knowledge". Can I suggest that you start by acquiring some other kinds of knowledge. Read some books about Christianity, especially those looking to explain Christianity to non-Christians. These books are called 'apologetics', and any church or Christian bookshop will have plenty.
Obviously being a Christian involves belief in God. You will need to come to a belief in God at some point in your journey. But don't start by 'assuming' his existence: examine the evidence and decide for yourself. Believing in his existence is also not necessarily the first step. I know people who started their walk with God by living a Christian life to the best of their ability, without necessarily believing in its truth. As the practice seemed to 'work' for them, that increased in them the belief that there must be a reality underlying the teachings.
The other important point is to seek out Christians and talk to them. That will give you a much better idea of what Christianity is like in reality, and whether it is real for those people.
Here is a to-be-saved step-by-step process for ya:
Belief in God (Or rather the acceptance of the possibility that God is real) - Though this doesn't save you. The devil knows God exists.
See God for what he is - Holy, pure, perfect. - For this, you can get to know God and his attributes through reading the bible (try starting with a gospel: Matthew, Mark, Luke, or John) and/or attending a biblical based church.
See your sins for what they are - Evil (use the 10 commandments)
a. Have you ever lied?
b. Have you ever said God's name in vain? (blasphemy)
c. Have you ever stolen from someone, even something minor?
d. Have you lusted for earthly things? (Idolatry)
e. Have you lusted for another human being out of sensual pleasure, or had sex outside marriage? (Adultery; see Matt. 5:28)
If you answered yes to any of those in #3 (and that is a short list), then you need to see that you are dead in your sins, and you have separated yourself from God and the kingdom of heaven. God, being perfect, cannot have liars, thieves, fornicators, blasphemers, etc. in heaven. Otherwise he would not be the just God that he is.
Know that God loves you and wants to spend an eternity with you. He has made a plan of salvation so that those who want to turn away from themselves and turn to God can do so. God literally became flesh, in the name of Jesus Christ, and took the punishment of your sin on the cross, so that whoever would repent of their selfish ways and put their faith and trust in God can have eternal life.
One thing that helps me desire God's will over my own is that I don't know what is best for me; not even close. God, being perfect, knows exactly what is best for me and also wants me to have as much joy and pleasure as I can possibly have!
Psalm 16:11 (KJV) - Thou wilt shew me the path of life: in thy presence is fulness of joy; at thy right hand there are pleasures for evermore.
Seems to me that the essential element of being a "Christian" is to believe in Christ, that is, to believe that:
You have broken God's laws. (Which implies that you believe that there is a God.)
There is a penalty to be paid for breaking these laws.
Christ has offerred to pay the penalty for you.
Accepting Christ's offer.
What leads you to such belief seems to me to not matter to the end result. That is, whether you believe because of careful study of historical, technical, or whatever evidence; because someone you trust told you so; on the basis of subjective feelings; etc. Just like, if someone offers you a tip on a stock that they say will make a bunch of money, to make that big profit you have to buy the stock, which implies that you believe it will make money or are willing to give it a try. Whether you come to that faith because of careful study of the company's financial reports, because you trust the recommendation of a financial advisor, or because you called the psychic hotline and they told you that W is your lucky letter for today and this company's name starts with a W, or whatever, if you buy the stock, you'll make the profit, and if you don't buy the stock, you won't.
