What does that mean?
Good question, friend.
In short, this is what the Bible teaches.
Romans 3:23 "For all have sinned, and come short of the glory of God." This is the first thing we should understand when it comes to whether or not we will go to heaven when we die. What this means is that we have all committed at least one sin in our life.
Sin is defined as the transgression of God's law. 1 John 3:4 "Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law." What this means is when God tells us not to do something, and we do it anyway, we break his commandments. If he tells us not to lie, and we lie, we commit a sin. If he tells us not to steal, but we steal anyway, we have committed a sin, etc.
The Bible teaches that sin entered into the world because of man, and not because of God. Romans 5:12 "Wherefore, as by one man sin entered into the world, and death by sin; and so death has passed upon all men, for that all have sinned." So the fact that we are sinners is our fault alone and not God's fault at all.
Because of the sin we commit, there is a penalty. And that penalty is death. Romans 6:23a "For the wages of sin is death;" So we earn this for ourselves and deserve to die for our sin.
But the Bible teaches not only of one death, but of two deaths. Revelation 20:14-15 "And death and hell were cast into the lake of fire. This is the second death. And whosoever was not found written in the book of life was cast into the lake of fire." This second death is the death of our soul. The Bible describes this death as everlasting punishment in 2 Thessalonians 1:8-9, so it's a punishment that never ends.
We die once according to Hebrews 9:27 and then are judged for our sins. According to God's law, all of us are guilty and deserve death, and we must come to accept this.
However, there's good news. God loves you, and doesn't want you to go to hell, so he sent his Son Jesus Christ into the world as God manifest in the flesh to live a perfect life without sin and to die upon the cross to pay the penalty for our sins. Romans 5:8 "But God commendeth his love toward us in that, while we were yet sinners, Christ died for us." So Jesus came and died that we could be freed from the debt we owe God.
The Bible says that Jesus dying on the cross is a free gift bought and paid for by God himself. Romans 6:23 "For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord."
Jesus died for everyone's sins according to 1 John 2:2 and is the sufficient payment for all. On the third day, Jesus rose from the dead as a show of grace from God the Father that our sins have been sufficiently paid for (1 Corinthians 15:3-4).
However, even though Jesus paid for the sins of the entire world, not everyone goes to heaven. The Bible asks one time what a person has to do to be saved, and the answer is found in Acts 16:31 which says, "Believe on the Lord Jesus Christ and thou shalt be saved, and thy house." It doesn't say that you have to live good enough for it, go to church for it, do any good works for it; it doesn't say that you can earn it or deserve it. All it says is to place your trust and faith in Jesus Christ, that he is the Son of God, and that he died for your sins, and rose again the third day. Whosoever believes in Jesus will never die, nor experience hell, but will have everlasting life (John 3:16). God promises that once you receive salvation, you will never perish (John 10:28) and no one can snatch you out of his hand, so you can have assurance that you're saved, because God promised you and he cannot lie according to Titus 1:2.
Once you realize all of this and believe it, a person calls upon the name of the Lord to receive salvation according to Romans 10:13. "Whosoever shall call upon the name of the Lord shall be saved."
And this is the way we do it according to Romans 10:9 "That if thou shalt confess with thy mouth the Lord Jesus, and believe in thine heart that God hath raised him from the dead, thou shalt be saved."
Do you desire to be saved?