The just shall live by faith

For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith. Romans 1:17

And so it is for anyone who claims to be a Christian. By faith we are saved from our sins. There are no signs, secret hand shakes, or good works to salvation; just believe that Jesus Christ died for your sins,was buried, and rose the third day, and you will be saved. It is guaranteed by God that with belief comes salvation from our sins. God further tells us in the Bible that belief in the Gospel of Jesus Christ is the only way to be saved from the punishment (eternally burning in Hell) for our sins.
How does one know they are a sinner?
It is simple enough to find out. All we need to do is look at the Ten Commandments.

You shall have no other gods before me. Exodus 20:3

So, do you worship only the God of the Bible? Do you deny God exists? Do you reject God? Do you worship any of the false gods, such as Buddha, Zeus, Allah, etc.
There is only one God. He exists in three ways; Father, Son , and Holy Spirit. He exists in all three ways at the same time. An example of this is at Jesus Christ's baptism.

And Jesus, when he was baptized, went up straightway out of the water: and, lo, the heavens were opened to him, and he saw the Spirit of God descending like a dove, and lighting upon him: And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.
Matthew 3:16-17

So we see in the above verses that all three ways God exists were present at Jesus' Baptism. This proves that God is not limited to existing in any of the three forms one at a time.

You shall not make to you any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth: You shall not bow down yourself to them, nor serve them: for I the LORD your God am a jealous God, visiting the iniquity of the fathers upon the children to the third and fourth generation of them that hate me; Exodus 20:4-5

Do you have any idols that you worship? This could be anything that you set in your heart above God.
We have just looked at only the first two commandments and if we are honest with ourselves we will admit that we have broken both of them. God tells us that the punishment for sin is death. He also tells us that we will burn in Hell for breaking His laws.
If you were to die today would you go to Heaven o Hell?
God tells us that if we believe the Gospel of Jesus Christ we will be saved from our sins and our punishment for them. All it takes is belief in the Gospel of Jesus Christ (Our God, Jesus, died for our sins, was buried, and rose the third day).
Believe and be saved!