Yeah, so I'm kindasorta having some difficulty understanding Catholicism..?

What you have so far sounds great. I would however not state that it caused the fall of Rome. The fall of Rome was more due to political corruption, barbarian hordes and the use of mercenaries that really didnt care about them. Catholisim was used as a pretense for war during the crusades. Also most peasants couldn't read or write and people would lie to them about what the bible actually says.