The Bible has God's rules of how we should act. When you don't follow God's rules, you sin against God.

So when you know the good things you should do and don't do them, you sin.
(James 4:17)

Yes. When you choose to disobey God, you don't feel close to God or happy with your life. Without God's forgiveness, punishment goes on after you die.

When you sin, the pay you get is death. But God gives you the gift of eternal life because of what Christ Jesus our Lord has done.
(Romans 6:23)

Yes. When you ask God for forgiveness and trust in His Son, Jesus, your sins are forgiven by God.

God loved the world so much that he gave his one and only Son. Anyone who believes in him will not die but will have eternal life.
(John 3:16)

To trust in or believe in Jesus means trusting Jesus to save you from punishment and choosing to follow Jesus' example. By the way Jesus lived, He showed us how to live in God's way and how to follow God's rules.

Do not let your hearts be troubled. Trust in God. Trust in me {Jesus} also.
(John 14:1)

We believe we are saved through the grace of our Lord Jesus.
(Acts 15:11)

The Bible says you must repent for your sins. That means you must be sorry for your sins. You must pray to God and ask God to forgive your sins. You must trust in Jesus to save you from punishment. Then you must promise to follow Jesus' example and do your best to live in ways that honor God.

But God is faithful and fair. If we admit that we have sinned, he will forgive us our sins. He will forgive every wrong thing we have done. He will make us pure.
(1 John 1:9)

If you love me, you will obey what I command.
(John 14:15)

Jesus said we must be willing to tell others that we are Christians. Jesus was baptized when He began to teach others about God. When we follow Jesus' example by being baptized, we show others that we have promised to live by Jesus' example. What about someone who says in front of others that he knows me? I will also say in front of my Father who is in heaven that I know him. (Matthew 10:32)

When you are baptized, you become a member of your church. The other Christians in your church were also baptized. Jesus said believers are to tell others about Him.

So you must go and make disciples of all nations. Baptize them in the name of the Father and of the Son and of the Holy Spirit. Teach them to obey everything I have commanded you. And you can be sure that I am always with you, to the very end.
(Matthew 28:19-20)