I want God to come into my life and forgive my sins; but how do I do that?

The Bible tells us that sin always, always, always brings death. It also tells us that we all have sinned. That means we're all in big trouble!
God made a plan to rescue people from the death that sin brings. Instead of you dying for your sins, Jesus died for them.
Your part is to accept Jesus as your Savior. That means you ask God to accept Jesus' death for you so that you won't have to die.
So, tell God that you are sorry for your sins and thank Him for His plan to save you from eternal death.
Ask Him to forgive your sins and to send His Holy Spirit to live in you to change you to be just like Jesus.
Ask Him to make you more and more like Jesus every day.
And then, ask God for the faith to believe that He will do what He has promised to do.
Now you need to know everything you can possibly learn about Jesus because the more you look at Him and learn about Him, the more the Holy Spirit can change you into being like Him.
In the morning—after the alarm clock rings or your mom or dad calls you, sit up and put your legs over the edge of the bed. (That's so you won't fall back asleep!) Before you do anything else, bow your head and say something like this, "Good morning God. Thank You for a new day. Help me to grow to be more like Jesus today. Help me remember to be kind and listen to Mom and Dad and my teacher and obey them. Help me to remember all day long that I'm Your child and that you will take care of me and keep me from sin. Amen."
If you aren't having worship at breakfast time, ask your mom or dad if you can start. A good place to begin is to read the book of Mark out of a children's version of the Bible. Just read a few verses or a story each morning and ask each other what you learn about Jesus in those verses. Then ask God to put those things into your life.
In the evening get ready for bed fifteen minutes earlier than you usually do. Then, in family worship or by yourself, read your Sabbath School lesson story and do one of the activities that is in the Bible Study Guide (quarterly). Be sure to memorize your memory verse. It is really fun to learn it by singing the memory verse song from the Sing-A-Long Memory Verses CD.
After spending time with God by studying your Sabbath School lesson, take another look at the message of the story. In Primary Treasure, we put a line that says, "This story can teach me that . . . ." Think about that message and what it tells you about God and worshiping Him and being a Christian and helping others. Then ask God to put that thing into your heart and life.