It's really pretty simple ... there's a God and only one God. In fact, He is the Creator of everything, and we're made in His image, which means we're like Him in many ways. And while many of us don't like it, He's God and we're not. He's loving and just and desires a relationship with us.
We're all born sinners, and we all make choices in life that separate us from God. Because we have free will, we can reject this relationship and live outside of God's plan for our lives. But God loves us so much, that he sent His only Son, Jesus, to die so we could live. The cost of sin is separation from God, spiritual death, but Jesus came and his death paid everyone's debt. Because of His perfect love, this gift from God is waiting for anyone who will receive it.
This is called Grace, and God gives it freely and abundantly. The choice is ours: to believe or not. Jesus said to Repent (change the way we think), Believe (pledge our allegiance to Him), and Follow Me (put into practice Jesus’ words and ways). If we decide to accept this grace, and to repent, believe and follow, God gives us new life, a life that extends beyond physical death.