A doctrinal summary will not tell you how the Catholic Church makes a decision. The structure is episcopal and monarchical at once, and the second half is what distinguishes it from every other church with bishops.
Every Catholic belongs to a parish, grouped into a diocese under a bishop who holds real ordinary authority there. Bishops are not elected locally; they are appointed by the pope, usually from names worked up through the papal representative in the country. That single fact does more to shape the church's behaviour than most doctrinal statements, because it means the line of accountability runs upward to Rome rather than outward to the diocese.
Rome itself governs through the Roman Curia, a set of departments handling doctrine, worship, bishops, clergy, religious orders, the eastern Catholic churches and the rest. Its judgements bind. Alongside it stands the college of cardinals, whose one irreducible function is to elect a pope in conclave on the death or resignation of the last. Law is codified: the Latin church has run on a Code of Canon Law since 1917, revised in 1983, and the eastern Catholic churches on a separate code since 1990.
Two counterweights exist and are genuinely contested in strength. The Second Vatican Council, sitting from 1962 to 1965, recovered the language of collegiality, the bishops as a body sharing responsibility for the whole church, and created a standing Synod of Bishops. National bishops' conferences were also strengthened. How much either can actually decide, as against advise, has been argued over ever since, and the argument is not settled.