'God' is a word everybody knows. 'God bless'.
'Thank God'. 'Oh my God'.
But who is God?

God is the Creator of the universe. He always was. He made the world, everything in it, and every person that ever walked the earth was formed by Him. He made you.

God is the ruler, the king, the boss. Because, well, He made it all. That means He makes the rules. Even if you don't know God, you know His rules. Do not steal, do not kill, and so on. God made the rules for right and wrong, and when He created the perfect humans in the garden of Eden, He understandably expected them to follow the rules. But they didn't. That left God in an almost impossible situation. Anyone who has sinned is automatically separated from God. Because He's perfect, and Heaven is perfect. And you can't have imperfect (and really messed up) people parading around a perfect eternity, having gotten in for free. Adam and Eve, along with every person who ever sinned, were automatically condemned.

But God is also Love. He loves each and every one of us as if we were the only ones on the earth. There was only one way that He, the judge of the universe, could allow you to stand before Him, guilty, and let you go. Someone else had to take the punishment.

And someone did.

The Son of God, Jesus Christ, who lived in heaven, in glorious paradise, and reigned over the entire world, gave everything up to come to earth, be born in a stable, and live as a poor man. He, in His holiness, lived just like you and I, only He had no home, nothing of His own, and most people hated Him.
Why? Because they did not want to accept that they were sinners
John
  chapter 1 tells us: "In Him was life, and the life was the light of men. And the light shines in the darkness, and the darkness did not comprehend it." The darkness was the sinful people.

So this man, Jesus, who for years walked from city to city, showing people that, even though they were sinners, they could still be saved, if they believed in Him. But they didn't understand.
After three years, the 'Pharisees', the political/religious leaders of the time, who for Jesus' entire ministry had hated Him for the things He said, finally succeeded in what they had wanted to do. They killed Him. Crucified Him. Now, the One Man, the Son of God, the only hope for mankind, was dead. And no one knew why God had let it happen.

It seemed like all hope was lost, but it wasn't. Because God raised His Son back from the dead three days later, and conquered death, because He was God. Then Jesus went back to Heaven 40 days later.

So what was the point? Why send Your Son, only to let Him get killed, only to bring Him back to life again? Because we were sinners, lost in our own sins, condemned to hell, standing before the judge (God). He, in His perfectness, said that because of our sin, we were going to die, and be separated from Him forever. But right there, Jesus, perfect, holy, and undeserving of death, stepped up and took your place. He took everyone's place. He was forsaken by God, and crucified, so that you didn't have to be, and so that we could be with God forever. Then, He conquered death, and separation from God, by rising again. He defeated Satan, and He defeated all evil.