Who killed Jesus? The full answer may surprise you, but is necessary to understand why the cross is important. The cross is a focal point of God's actions in human history to reveal himself, and save us from ourselves.
Whether we encounter the gospel of Jesus as children in church or in a presentation from an enthusiastic Christian, we may only absorb a few pieces of the whole thing.
The Apostles' Creed lays out all the basics in a short outline, and is affirmed by almost every Christian church in history.