How is the once-given Revelation passed on to you and me? God spoke to the prophets and as our Incarnate Lord, but how does that speech, how do those deeds, get passed on to you and me? How do we come to learn of them?
Through Scripture and Tradition. These are the Two Sources of Revelation. The Magisterium is the interpreter of these two sources. (Note: An earlier version stopped at about 36 minutes. Apparently, the file was too large. I’ve fixed this.)