It's really pretty simple ... there's a God and only one God. In fact, He is the Creator of everything. We're made in His image, we are His children. As our Abba Father (loosely translated "daddy"), God loves us beyond what we can imagine, and he 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 the relationship that God wants to have with us and live outside of his 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 (turn away from ourselves and toward him), believe (enough to trust him), and follow (put his words and ways into practice). God knows that none of us will get it right all the time, but if we choose to accept this grace, and to repent, believe and follow, God gives us new life that extends beyond physical death.