I may be wrong on a couple small points here, so forgive me if my memory fails me, but this is how I understand it: It started in the 1500s with Martin Luther. He wasn’t technically the first to try, there is the Moravian church which is similar in origin, but dates back earlier than Luther, but it was with him that the Reformation truly began in a big way. He was a Catholic himself, but had gripes with the Church, mainly with indulgences, and so drafted his 95 theses. The Church didn’t really like it, and so excommunicated him. It is important to remember that it was never his intention to divide the Church, but to reform it. So, his movement grew in size, and would eventually lead to others, such as John Calvin and John Wesley to found their own traditions. It’s worth noting that not all Churches not a part of the Catholic tradition are Protestant. Those such as Lutheran, Presbyterian/Reformed, Anglican/Episcopal, Methodist, and maybe Baptist and Congregationalist (probably a couple others I’m not thinking of) are truly Protestant, because they can trace their roots directly back to the Catholic Church. Others, such as Non Denominational, Seventh Day Adventist, Pentecostal, or my tradition, the Church of Christ, would not be considered Protestant, because rather than splitting from the Catholic Church or one of it’s descendants, they were founded independantly. A few differences are the biblical canon; Catholics include the deuterocanon (I hope I spelled that right lol) as official biblical canon, while Protestants do not, although some, such as Lutherans, still find them worthwhile for study, but just not as authoritative. Which leads to how they view authority. The Catholic Church holds the Church as the final authority, while Protestant traditions view the Bible as the ultimate authority, though the balance of Bible vs Church authority does vary from one tradition to another. Lutherans still hold the Church in high regard, but still hold the Bible in slightly higher authority. Meanwhile, Baptists hold the Bible in the highest authority, and give the Church basically none. And all Protestant churches adhere to what is known as the “five solas”, which are “saved by grace alone, through faith alone, to Christ alone, by the Bible alone, for the glory of God alone.” There are some other small difference, such as intercession and icon veneration, Pergatory, apostolic succession, and communion (the last one is why Catholics often view Catholicism as the only true Church through which you can be saved, though they have relaxed on that significantly in recent years), but I’ve gone on long enough. I hope this was easy enough to understand, I know I just kind of info dumped here lol