Diving right into studying civil and canon law after being ordained, Paul VI (then Fr. Giovanni) spent most of his time serving the Church at the Vatican under Pius XI and Pius XII.  He worked in the office of the Secretary of State some of his responsibilities include helping refugees and Jews during WWII and teaching at one of the local Universities for a time.  It was not until he was named Archbishop of Milan in 1954 that he had his first pastoral role. In that role he evangelized on issues such as immigrants and materialism. After election to the papacy, Paul VI chose to continue the council convoked by his predecessor encouraging the leaders to be open to modern world but to hold fast to the Church fathers and Church Tradition.  When he concluded it 3 years later, he also oversaw the beginning of its implementation.

His encyclical, Humanae Vitae, upheld the Church's teaching that the marital union must be unitive (loving act between a married wife and husband) and procreative (open to life).  He denounced artificial contraception and abortion while promoting the use of Natural Family Planning to responsibly plan family growth. He spoke of the pitfalls that would surely follow if artificial contraception and abortion and the disregard for the holiness of the marital union was not respected; these are seen as prophetic by many.

Beyond these two well known aspects of Paul VI's life, he also was the first pope in over a century to leave Italy.  He visited six continents (including the United States) and wrote extensively on the dialogue of salvation and the development of peoples.  He also instituted the World Day of Peace.  

He also loved to share the joy of the faith with young people.