Peter and John were two of the twelve apostles (Mark 1:16-17) that were ordained by Jesus Christ to help run his church (Luke 6:12-16, Ephesians 2:20).
In their early normal lives, Peter and John were fisherman. Until one day after witnessing a miracle, they were convinced that Jesus Christ was the Messiah, and eagerly dropped all their things to follow him (Matthew 4:18-22).
Jesus Christ called twelve men called apostles to help organize his church, giving them all power and authority to do mighty miracles and preach his gospel (Matthew 10)
Peter, James and John were given special powers by Jesus that the other apostles didn't yet have.
Peter especially was given priesthood keys that allowed them (the apostles) to bind and seal things on Earth and in Heaven (Matthew 16:19) this officially made him (Peter) the leading apostle when Jesus Christ was killed.
Peter ran the church after Christ died, but the people hated the Apostles just like they hated Jesus Christ. And one by one all (with the exception of John) were killed as Jesus predicted would happen to them, Peter included (John 21:18-19, Matthew 24:9, Fox's The Book of Martyrs)
John still lives to this day, continuing the Lord's work, as this scripture suggests (John 21:22-23)
John is the Apostle who wrote The Gospel of John, The Epistles of John and Revelations in The Bible. He is NOT John the Baptist, as many people confuse him with
Fox's The Book of Martyrs