There are four Gospel accounts: Matthew, Mark, Luke, and John. Written under the inspiration of the Holy Spirit, they are the only accounts to give us the authoritative and infallible record of the life of Jesus Christ. Two of them were written by apostles who were eyewitnesses to the earthly ministry of Jesus. The other two writers were not apostles but men who consulted eyewitnesses when they wrote their accounts.
All four Gospels were written to provide a foundation for the faith of those who would believe in Jesus the Messiah. And each Gospel was written in response to a need.
The earliest need for a Gospel arose among the Jews because the Good News first went to Jerusalem and Judea. Matthew was written to explain to the Jews that Jesus was the promised Messiah, the King of Israel.
The second group to be reached with the gospel was the Greeks. Luke wrote his Gospel for the Greek world, which had been reached through the ministry of the apostle Paul. Converted Gentiles too needed a foundation for their faith, and Luke presents the life of Christ in a way that portrays him as the perfect man.
Mark, the companion of Peter, wrote his Gospel to the Roman world, the third segment of society that was reached with the Good News. He wrote to present Jesus as the Suffering Servant.
These three Gospels are referred to as the "Synoptic Gospels" because they present a common viewpoint of the life of Christ.
John wrote a universal Gospel to present Jesus Christ as the Savior so that men and women might come to believe in him and have eternal life. No Gospel has a higher Christology than his. Jesus, the Word, has made God known. He can reveal the Father because he is Deity.
And so we have four Gospels. Please don't let anybody make it more complicated to you than this.