The LDS have “official teaching” manuals for the teaching of their beliefs. They can be easily found online with a simple google search. Here are a couple of points:
The Bible
Catholics & Christians believe the bible is the word of God. While Catholics retain 7 more books of the bible that were taken out after the reformation, all still believe the bible is the word of God.
The LDS say the bible is true as far as correctly translated leaving room for them to change it in a way that supports their belief system. They also created other “scripture” such as the Book of Mormon. They believe their “scripture” is just as important as the bible.
Marriage
The LDS still believe in polygamy. While many of the mainstream LDS don’t practice it on earth (although many sects do) they believe marriage is eternal. For a man to earn a higher place in heaven he needs more than one wife. But this belief is completely different for women. A man can be “sealed” to several women on earth if widowed or divorced, but a woman may only be sealed to one man. Single women or female children who pass away before being able to married or “sealed” are assigned to men in their version of heaven. For those who are adults and unmarried there is a certain less than attitude among others.
As Christians we believe marriage is a vital sacrament for those called to marriage and also recognizes that not everyone is called to married life even if they are not called to a religious vocation. We believe marriage is intended for our lives on earth and when a spouse passes away the living may remarry if they choose. (Aside from Permanent Deacons) But married or single our ability to go to heaven is not based on someone else’s status within the church.
Christianity
The LDS claim to be Christians which is a fairly recent change. The two links below should give more information than I can at this time.
christianitytoday.com/ct/2016/june-web-only/mormons-and-christians-so-close-yet-so-far-away.html
patheos.com/blogs/bibleandculture/2012/08/27/why-mormons-are-not-christians-the-issue-of-christology/
Catholics are Christians and recognize most protestant baptisms as valid. I was baptized as an infant in a mainline protestant church and when I converted I did not need to be baptized again. The LDS does not recognize any other baptism as valid. If they were Christian wouldn’t they believe a baptism in the proper form and matter would be valid?
Revelations
The LDS believe their prophet is capable of receiving revelations and being able to change theology based on that revelation. Two significant revelations came at very opportune times in history. When Utah wanted to become a state in the US it was blocked because of the practice of polygamy. Then the prophet had a revelation that polygamy was not an acceptable practice after all and Utah became a state. Until the civil rights movement blacks were not permitted to the “priesthood” (not the same as a Catholic priest) because of their color. There was the belief dark skinned people were evil and God gave them dark skin so the good LDS could tell who was good or bad. Then came the civil rights movement and once again a revelation from the prophet. This time saying that part of “scripture” (going back to their own created scripture) was wrong and blacks were then allowed to be in their priesthood.
Catholic believe all revelation is complete and has been since the 1st century. People can and do have private revelations which are sometime accepted by the church, Fatima, Our Lady of Guadalupe, Lourdes and so on but none that will change church Dogma or Doctrine.
There is so much more out there regarding the difference between the Catholic Church and the LDS. You self identify Christianity as your faith. Please stay Christian. The LDS offer all kinds of feel good stuff right away and want you to be baptized right away. Then after than you can learn what the LDS teach. On the other hand the Catholics want to teach a lot about what we teach and believe and then make a completely free and informed choice.