The differences are too many to list here. Better to ask what they have in common, and that would be that they're both loosely based on the same religious personality, Jesus. Other than that, not much.
We believe in the Jesus Christ of the Bible and Book of Mormon, they both teach the same thing about Christ so it's the same Jesus Christ, while Catholics believe in the Christ of tradition, not the Biblical one. The Church of Jesus Christ of Latter-Day Saints is Jesus Christ's true church on the earth. The head of the Catholic Church is the Pope while the head of The Church of Jesus Christ of Latter-Day Saints is Jesus Christ. It is the only church on earth that has the authority to do things in Jesus Christ's name. Like the Pharisees, the Catholic Church believed in dead prophets yet deny the living prophet of God. We know there is a true living prophet of God on the earth.
We're both Christian sects, so of course we share the basic beliefs of Christianity: belief in God, in Christ as our Savior, in the Bible, etc. There are, however, obviously differences, though since I'm not Catholic, I'm not the best source of Catholic doctrine. You should ask an actual Catholic (and if I'm wrong, Catholics, please correct me...and nothing I write is a reflection on Catholic beliefs in any way. I'm not criticizing, just pointing out the differences as best I understand them).
Catholics (and this is very generalized, as there are obviously more than one set of Catholic beliefs out there):
Are Trinitarians (God and Christ are one being), sometimes pray through Mary, that judgment comes immediately after death, that those who were not baptized cannot be saved, and that infants who die before baptism either go to hell or are sent to limbo.
Mormons:
Believe God and Christ are one in purpose but not in body, don't believe in Original Sin (the idea that we're born as sinners. Mormons don't believe that anyone is ever accountable for any sins but their own, so we don't believe infants are held responsible for the choices of Adam and Eve. In fact, we believe Adam and Eve were transgressing, not actually sinning, when they ate the fruit). We don't practice infant baptism, either, instead waiting until children are at least eight years old and can decide for themselves. Those who die before that are still innocent and so are accepted unconditionally by God. Our beliefs on the afterlife are a bit more complicated than just heaven or hell, but we also don't believe that we're judged IMMEDIATELY after death. Instead, we believe that there's a period in between death and the resurrection, when those who knew and followed Christ teach the gospel to those who did not, thus giving everyone one final and completely equal opportunity to accept Christ. Those who died without baptism can still accept Christ in the next life, and though they still need to be baptized, we do that by proxy on their behalf.
Um...both groups have leaders, the Catholics following the pope, Mormons following a prophet. We have more similarities than differences, but I think those are the basics. I didn't go into very much detail on Catholic doctrines simply because, again, you'd need to ask a Catholic, but I hope that at least gave you a place to start.
From a practical point of view, most new LDS converts come from a Catholic background.
They also are the most righteous and pious Mormons, after they convert.
They can't help but import a lot their previous beliefs, as they join THE Church Of JESUS CHRIST Of Latter Day Saints.
The LDS Church is about one thing. Living the commandments of Jesus Christ. So therefor variations in certain specific esoteric beliefs are less important, than in some other religions.
Opinions may vary, but righteousness is always the same. In other Churches that concept is often reversed, and the only thing they have going for them is theological disputes.
Any theology that does not lead to being the Good Samaritan in some way, is a waist of Theological energy.
Mormons believe in living the Commandments of Jesus Christ, the more the better. The better this is done in this life, the higher level in Heaven the adherent will eventually go, in the after life, because God is perfectly just.
Because people are stupid and make mistakes and sin, that is what Jesus Christ came to help out with. But a person needs to come half way.
Without faith/works, God's mighty power remains dormant, and unfilled potential waits to be tapped. And it never will, unless that person repents, and follows the commandments of Jesus Christ, like climbing the stairway to Heaven, more and more each and every day.
Reaching the highest level of consciousness is what THE Church Of JESUS CHRIST Of Latter Day Saints is all about. And that can be done by building better habits one by one by one.
Just like climbing the stairway to Heaven... each step being another good habit gained, or another bad habit gotten rid of.
With God nothing is impossible, so there is no reason not to think, that anyone, as long as they are persistent, and as long as they refuse to quit, will not attain the highest level of consciousness, in this life, the Christ-Consciousness.
This is done by living all the commandments of Jesus Christ completely. The more the better. The closer to the Christ Consciousness a person gets is dependent on living the Commandments of Jesus Christ.
Catholics obviously by and large are less concerned about living the commandments of God, then Mormons are.
There is no death bed repentance concept in LDS doctrine. Better late then never, but that is not the same as fully repenting in this life, when it can really make a huge affect on what Heaven that you go to in the Afterlife.
People think that money is what is important in this life. But every act of Good Samaritanism will be worth more than all the gold in all the World, when this life is over, and judgment day comes, and all who lived are judged by Jesus Christ.
This shows how important people are and how relatively unimportant everything else is. The commandments of Jesus Christ is all about people, and being righteous, and being good to people, fellow human beings, children of God one and all.
Of course there are many good Catholics who are converting and becoming Mormon, because increasingly what Mormons are saying to them is making a lot more sense then what their Catholic Priests are saying to them.
Right now there are 15 million Mormons in the World (approximately). In twenty years from now, there will be 35 million Mormons in the World... most of those will be former Catholics, as far as people who convert, and most of those will come from South and Central America, though some will come from places like Eastern Europe, and the Philippines, etc.
Still that is only a small percentage of what the number of Catholics will be, numbering over a Billion at the present time, and surely they will number more in twenty years time, than what they are now, then.
Even though the number of Mormons is relatively small, the rate of expansion is the most of any Major Christian religion in the world.
The Book Of Mormon The Second Witness Of Jesus Christ, is destined to the be the most influential Christian religious Book in world, with the exception of the Bible.
LDS Churches are open to visitors, and visitors are welcome, worship services are on Sunday.
If you want to know more about THE Church Of JESUS CHRIST Of Latter Day Saints, then going to an LDS Church, would be a good first step.
a religious question what is the difference between the catholic and mormon religions
