The gospel is the key to a relationship with God. The word gospel simply means good news. If there is good news then there must be bad news. The bad news is that everyone on earth has broken the perfect standard of God, we have all fallen short of His standard. This is called sin. This sin deserves a punishment.
The Bible says that the wages of sin is death. This means that because of our sin we experience an earthly death and more crucial, a spiritual death. We will be forever separated from the God that loves us and wants a relationship with us.
The good news is that God made a way for our sin to be paid for. That way is Jesus Christ. Jesus Christ is the son of God who came down to earth, lived a perfect life, the life we were meant to live, and died a horrible death on a cross, the death we were suppose to take. Three days later Jesus rose from the dead proving that He has conquered sin and death.
Now because Jesus took the punishment of sin upon himself we can be made right before God. If we trust in Jesus, and make Him the Lord of our lives, then we can have a relationship with the creator of the universe, and be saved from our sin.