Just wrote some stuff on the differences between Catholics and protestants in beliefs regarding 3 of the solas, figured i'll just post em here. There's a catholic bias of course but it shouldn't be too bad.
1: Sola Scriptura
Protestants believe that only the scriptures, as in, the bible alone is authoritatively binding for what Christians should believe. This is in distinction to Catholics, that hold that the bible, the traditions of the church, and decrees from the councils (as in, ex cathedra statements from the Pope) are authoritatively binding. To expand further, Catholics believe all Catholic beliefs that have always been held universally by all Catholics everywhere - as in what is tradition - is infallible, for "the gates of hell shall not prevail", and under their logic for even one doctrine to be in error would mean hell has prevailed. The nature of the differences is obvious, protestants reject Catholicism, and therefor necessarily must reject the idea that God appointed a Pope, so obviously they can't rely on their councils or traditions. In the other case, Catholics who see the Pope as legitimate successors to the office given to saint Peter will have no problem accepting their authority in governing and direct the church, whether they like the current Pope or not.
Personally, I would sum up this as a question of "do you accept the human authority that God appointed to rule the church, or do you not believe that God appointed a man to rule the church, and therefor believe that the catholic church has no authority." It's pretty essential to not believe in the papacy as a protestant, because the pope, and in fact the whole Catholic church has long since declared Protestantism a heresy, which would mean you're heretic pretenders, destined for damnation if you do not recant… if they are right!
2: Grace alone
The biggest difference between protestants and Catholics is found most directly in the solas of grace alone, not the concept of faith alone - yet everyone spends so much time focusing on faith alone, which is confusing. In Protestantism, the concept of grace alone is the idea that you are saved not because you yourself are actually without sin, but because Christ died as the sacrificial scapegoat that pays the price that you deserved to pay. In other words, you are saved because of God's grace, not of anything you did - nothing about you made you earn your salvation to any degree. You're all sinner without any of the debt.
In Catholicism, Grace is absolutely essential for salvation, but it is not by grace alone. It is essential because we're all children of Adam born with original sin - this would damn everyone to hell no matter what they did; in fact it is orthodox belief that even the old testament saints were not able to go to heaven until Christ died (look it up). This is because for Catholics, baptism cleanses you of all your sins, including original sin, as though you were a completely new person or "born again" - this is what Christ's sacrifice did, as in it's not a legal payment to your account while you yourself are left a sinner; you are actually without any sin after baptism, but you can still sin and lose your salvation! You can and do still sin after baptism even though you are cleansed because of what they call 'concupiscence', which is your learned tenancy to sin that was never removed.
But this leads me to the most important point of all; for a catholic to be eligible for heaven, they must actually be without severe sin before they die, as in Catholics do believe it is possible to live without sin or "failure", "crookedness", and "iniquity". So it is by grace we get to heaven, as no one by their own bootstraps can lift themselves out of original sin, because in practice God is the one who must reveal himself to you, and because of many other practically essential graces such as the sacrament of confession (which is method of getting sins removed after baptism, however unlike baptism you do have to pay for these sins by purgation Isaiah 6:6-7), but that doesn't mean sit back and do nothing. we absolutely must work to be holy, without sin before we die, for that after that we cannot do anything to fix our state, and we must pay penance for our crimes and if you're feeling charitable, the crimes of others, be it this world or the next.
On a side note If you do not believe in free will, you'll probably like grace alone, because having a free will is not necessary for grace alone to work - it is a fact of history that Luther himself didn't believe in free will.
