The true church of Jesus Christ "subsists in (subsistit in) the Catholic Church, which is governed by the successor of Peter and by the bishops in communion with him" (CC, 816). This is because:
"it is through Christ's Catholic Church alone, which is the universal help toward salvation, that the fullness of the means of salvation can be obtained. It was to the apostolic college alone, of which Peter is the head, that we believe that our Lord entrusted all the blessings of the New Covenant, in order to establish on earth the one Body of Christ into which all those should be fully incorporated who belong in any way to the People of God" (CC, 816).
What is the relationship of other professing Christians to the Roman Church?
"Those who believe in Christ and have been properly baptized are put in a certain, although imperfect, communion with the Catholic Church" (CC, 838).
What of the fate of those who've never heard the gospel?
"Those also can attain to everlasting salvation who through no fault of their own do not know the gospel of Christ or His church, yet sincerely seek God and, moved by grace, strive by their deeds to do His will s it is known to them through the dictates of conscience. Nor does divine Providence deny the help necessary for salvation to those who, without blame on their part, have not yet arrived at an explicit knowledge of God, but who strive to live a good life, thanks to His grace. Whatever goodness or truth is found among them is looked upon by the church as a preparation for the gospel" ('Dogmatic Constitution on the Church'). See also CC, 839-848.
As for the hierarchical structure of the church, see CC, 874-892.
The Bishop of Rome (Pope)
The College of Bishops