Before we were born we were invited to a big meeting in heaven where we learned about Heavenly Father's plan. We learned that the earth would be created and that it would be a place where we could come and have physical bodies.
Part of Heavenly Father's plan was for us to learn to choose between right and wrong. He knew that we would sometimes make mistakes and that someone would have to pay for them. He chose Jesus Christ to be our Savior. Jesus would give his own life to pay for our sins so that we could return to live with Heavenly Father after our earth life.
There was another spirit person there who wanted to take away our agency and force us all to follow him. That was Lucifer, or Satan. He didn’t want to follow Heavenly Father’s plan—he wanted his own plan.
Everyone who is here on earth decided to follow Heavenly Father's plan. Each of us has been given a body to take care of while we live on earth.
When we left our pre-earth life, Heavenly father placed something called a veil across our minds so that we would not remember what had happened before we were born. That way, we could learn to have faith in Him and Jesus Christ, to control our minds and our bodies, and to obey the commandments and choose the right.
I know that I chose the right plan before I came to earth. I know that if I continue to Choose the Right that I can return to live with Heavenly Father again. I know that Jesus Christ is our savior and that he died for our sins.