The gospel or "good news" is that God created an opportunity for us to be reconciled to Him through the death and resurrection of His Son Jesus. (Romans 8:34).

The sacrifice Jesus made is what provides the opportunity for man to be reconciled to God.
This sacrifice pays the price in full for every sin of every person (1 Peter 3:18).
Does this sacrifice just apply itself to everyone automatically?
No, you were created with a free will and must accept the gift of God.

Embracing who Jesus Christ is as the Son of God, God the Son, the Messiah, is the most important thing you could ever do. A combination of putting your trust in what Jesus has accomplished through the cross and confessing what you believe sets everything into motion. This act of faith begins your spiritual journey and relationship with God.

It's important to note that believing unto salvation is not just a prayer you pray, but a total surrender of your will to God's will. This surrender is a submission to the Lordship of Jesus Christ which includes living according to the teachings of Jesus (Matthew 28:19).