Pope Benedict XVI
Insight and Understanding
For a brief explanation of the Church and the role of the Pope, the Catechism of the Catholic Church teaches the following:
The Church is ultimately one, holy, catholic, and apostolic in her deepest and ultimate identity, because it is in her that "the Kingdom of heaven," the "Reign of God (Rev. 19:6)," already exists and will be fulfilled at the end of time. The kingdom has come in the person of Christ and grows mysteriously in the hearts of those incorporated into him, until its full eschatological manifestation. Then all those he has redeemed and made "holy and blameless before him in love (Eph. 1:4)," will be gathered together as the one People of God, the "Bride of the Lamb (Rev. 21:9)," "the holy city Jerusalem coming down out of heaven from God, having the glory of God (Rev. 21:10-11)." For "the wall of the city had twelve foundations, and on them the twelve names of the twelve apostles of the Lamb (Rev. 21:14)." 
When Christ instituted the Twelve, "he constituted [them] in the form of a college or permanent assembly, at the head of which he placed Peter, chosen from among them (LG 19; cf. Lk 6:13; Jn 21:15-17)." Just as "by the Lord's institution, St. Peter and the rest of the apostles constitute a single apostolic college, so in like fashion the Roman Pontiff, Peter's successor, and the bishops, the successors of the apostles, are related with and united to one another (LG 22; cf. CIC, can. 330)."
The Lord made Simon alone, whom he named Peter, the "rock" of his Church. He gave him the keys of his Church and instituted him shepherd of the whole flock (Cf. Mt 16:18-19; Jn 21:15-17). "The office of binding and loosing which was given to Peter was also assigned to the college of apostles united to its head (LG 22 § 2)." This pastoral office of Peter and the other apostles belongs to the Church's very foundation and is continued by the bishops under the primacy of the Pope.
The Pope, Bishop of Rome and Peter's successor, "is the perpetual and visible source and foundation of the unity both of the bishops and of the whole company of the faithful (LG 23)." "For the Roman Pontiff, by reason of his office as Vicar of Christ, and as pastor of the entire Church has full, supreme, and universal power over the whole Church, a power which he can always exercise unhindered (LG 22; cf. CD 2, 9)."