The major differences between Protestants and Catholics is in two things, salvation and authority.
Salvation - It is a very hard thing (in my opinion) to concisely illustrate the differences in the two viewpoints on salvation. Suffice to say that most Protestants claim that Catholics think you need to do good works to be justified, and that this is unbiblical. This is not entirely true, and you’ll find that the differences in justification are not as great as most Protestants believe them to be. In my opinion the biggest difference in the two viewpoints is when you are justified, as opposed to how you are justified.
Authority - Catholics believe that there is a three-legged stool of authority with one leg being Scripture, another Sacred Tradition and the third the Magisterium (the pope). Protestants reject most tradition (it seems to me that they pick and choose which tradition to keep, for example they choose to keep the canon of the New Testament of the bible and for some unknown reason they take the Jews Old Testament of the bible) and they also reject the Magisterium and claim that the Bible is the most authoritative thing. This would be a good system except that history has shown how bad it actually is. Even from the time of the Reformation, rejecting the authority of the Church has resulted in countless interpretations of the Bible; some of them bizarre. Some people claim that there are 20 000 Protestant denominations today. I don’t really care how many there are, but even if there are 20 that is too many. The Protestant formula does not work. Indeed, if you are so opposed to same-sex marriages and female ministers then I suggest you join the Catholic Church. That is the only way to guarantee that your Church will continue to oppose these things.
Also realise that those people who are condemning Baptists are in the wrong. It is wrong to persecute somebody, no matter what their beliefs are. Catholics believe that other Christian denominations contain parts of the Truth, but to come to the fullness of Truth they must come home to Rome. Therefore some other denominations (and indeed other religions) do actually have some good in them, they’re only lacking the full Truth.
Purgatory is an interesting example as in my opinion it seems to be a huge tick in the favour of Catholics and Orthodox Churches. Both of these Churches have believed in purgatory since Christ was on the Earth, and I think that Orthodox Jews believe in purgatory as well? I’m not so sure about this. But I am sure that there are some Jews that pray for their dead for (I think it is) 11 months after they have died. There is some good evidence in what Protestants call the Apocrypha (what Catholics call the Deuterocanonicals) for purgatory and I have a theory that one of the reasons that the Reformers removed the Deuterocanonicals from the Bible was due to the reference to purgatory, since purgatory doesn’t really seem to square with Protestants theories on justification.
To conclude I will make the claim that the Catholic Church has been around since the time of Christ. The Protestant Churches have only been around since the Reformation, and many of them contain practices that can easily be shown to be false by studying the history of the Church. Jesus desired unity in his followers and the only way to obtain this unity is for the Reformers to come back home to the Catholic Church. Now if you are thinking that Protestants may be correct, I will set you a homwork question
How can you know which books belong in the Bible, without Sacred Tradition? Be sure to include reasons why the book of Mormon (for example) should not be included, as well as why other books of New Testament times (such as the Didache). Also give reasons as to why books such as the book of Philemon should be included in the New Testament. Information on this is plentiful on the internet, but make sure to research a large number of sources - both Catholic and Protestant alike - to obtain an answer. Have fun