Catechism of the Catholic Church §886 — excerpt
"The individual bishops are the visible source and foundation of unity in their own particular Churches." As such, they "exercise their pastoral office over the portion of the People of God assigned to them," assisted by priests and deacons.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: LG 23 · CD 3