Everyone has sinned. Unless you are perfect, you have sinned.
Rom 3:23 For all have sinned, and come short of the glory of God
What happens if you sin?
Rom 6:23 For the wages of sin [is] death; but the gift of God [is] eternal life through Jesus Christ our Lord.
I'd like to clarify things a little bit here. This verse is not of course referring to physical death. It refers to spiritual death, or separation from God. If you are still separated from God even after your physical death, you will not be in Heaven with him.
Psa 9:17 The wicked shall be turned into hell, [and] all the nations that forget God.
Rev 20:15 And whosoever was not found written in the book of life was cast into the lake of fire.
God doesn't force people into hell, people choose to go to hell of their own free will when they reject God in their life and commit sins. God doesn't want anyone to go to hell, that's why he offers us a way out. God tells us not to do certain things which are sinful because those are the very things which will put us in spiritual danger! That is why God has told us what is right and what is wrong. Sin separates us from God's protection!
You may think of yourself as a good person. Surely God would not let a good person get into hell, right? Well what you think of as good, is not really all that good. When you compare yourself to other people, you may seem to be a very good person, but when you compare yourself to God, you are certainly not more righteous than He is. The smallest sin is enough to bring a separation that can only be bridged through the Blood of Jesus.
Isa 64:6 But we are all as an unclean [thing], and all our righteousnesses [are] as filthy rags; and we all do fade as a leaf; and our iniquities, like the wind, have taken us away.
You have sinned, we all have, but there is a way to make things right.
Romans 10:9-10, "That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation."
Jhn 3:16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
How do we know Jesus is the only way to make things right with God? This is what Jesus said:
Jhn 14:6 Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.
Things are right with God, all you have to do is pray and tell God that you believe that Jesus shed his blood for your sins to be washed away. That's all you have to do! God doesn't care if you're poor, rich, if you've sinned a little or sinned a lot. God loves you and He wants you to live forever with Him.
It can be as simple as this:
"God, I know I have sinned, and I ask you to forgive me for those sins, as I accept that the Blood of Jesus has washed them away. I believe that Jesus died on the cross for my sins and rose again. I claim the inheritance that Jesus has left to me, the inheritance of eternal life. Let me be clean in your eyes, and send your Holy Spirit into my life."
After you have prayed, you should tell someone! The Bible says:
Mar 16:15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.
Links:
Ask and it shall be given, Seek and ye shall find, Knock and the door will Open. This is one of the best explanations of the need for salvation and how to acquire it that I have come across.
Another page where you can find the Sinner's Prayer.