2.18 How did things proceed after Pentecost?
At Pentecost the Apostles received the Holy Spirit, who inspired them and told them what to say and do. They went out into the world to preach the message of Jesus, the Gospel. They established Christian communities in many cities.
Peter went to Rome and became the leader of the local Church there. Many Apostles preached the Gospel among the Jews, while the Apostle Paul brought the message to the Gentiles, i.e. the non-Jews or heathens. Jesus’ Gospel is intended for everyone!
> Read more in the book
This is what the Church Fathers say
The Apostles... went forth into the world, and preached the same doctrine of the same Faith to the nations, and forthwith founded Churches in every city, from whence the other churches thenceforward borrowed the tradition of the Faith and the seeds of the doctrine, and are daily borrowing them, that they may become Churches. [Tertullian, The prescription of heretics, Chap. 20 (ML 2, 32)]