Matthew's Gospel (good news) is in the Bible's New Testament.
Matthew knew well the Bible's Old Testament. In the past, God appointed people (called 'prophets') to write about the future. Many prophets described Jesus' life and work. The things that the prophets wrote actually happened during Jesus' life on earth. Matthew explained this to prove that Jesus is the Christ. (The 'Christ' means God's king. The prophets said that the Christ would save us from the punishment for our evil deeds.)
Matthew's Gospel is a book about Jesus' life. Matthew wrote about the things that Jesus taught. His book includes a speech by Jesus, in Matthew chapters 5-7. This speech is called 'The Sermon on the Mount'.
Matthew's Gospel also explains that Jesus cured many ill people. Jesus caused blind people to see again (Matthew 20:29-34). He caused deaf people to hear again (Matthew 11:5). He freed people who had evil spirits (Matthew 8:28).
But some important people hated Jesus. They killed Jesus on the cross. But Jesus knew that this would happen (Matthew 16:21). The prophets had written that the Christ would die (Isaiah 53; Matthew 12:40). When Jesus died, he suffered the punishment for our evil deeds (Matthew 20:28, Matthew 26:28).
But Jesus did not remain dead. God caused Jesus to live again (Matthew 28). And Jesus is alive today, in heaven.