Jesus was a man who lived in Palestine about 2000 years ago, with years on our calendar roughly marked from his life. He was a teacher who was put to death by crucifixion in Jerusalem. Biographies of his life are provided in the Bible in Matthew, Mark, Luke, and John. Other material outside the Bible refer to Jesus, notably Josephus. There is little doubt that a man named Jesus existed in Palestine roughly 2000 years ago.
Christians believe something much more about Jesus. Beside being a man, Jesus also is God. Herein lies one of the great mysteries of Christianity: How can a man be God and still remain a man? Christians believe that Jesus came to earth to die. His death provides a payment for the sins and shortcomings of humans. As a sign of his power over death and sin, Jesus rose from the dead.
Christians also believe that Jesus is King. The whole world was created by God and it is his to do with as he pleases. Jesus will come back to judge the world. Those who believe in him will spend eternity with him.