This provides some fundamental information to explain Stem Cells and Cloning and what the Catholic Church teaches, including references for you to search further.

A stem cell is a unique type of “blank”, or unspecialized cell (also called undifferentiated), which is capable of renewing itself and becoming another, more specialized cell type, such as skin, muscle or nerve. They function to naturally replace or heal damaged tissues and cells in the body.

There are two broad types of stem cells: Adult and Embryonic.

Adult stem cells are found throughout the body, present in bone marrow, liver, epidermis, retina, skeletal muscles, intestine, brain, & fat. Some come from pregnancy-related tissues, such as umbilical cords, placentas, and amniotic fluid. 

Embryonic stem cells are obtained by harvesting live embryos which are generally 5-7 days old, and left over from in-vitro fertilization. When the stem cells are removed, the embryo is destroyed and the person is killed. Embryonic stem cells can also be obtained from miscarried or aborted babies (called “germ” cells).

Embryonic stem cells appear to be able to differentiate into any cell type in the body, but they are difficult to do so uniformly, are usually rejected by the recipient because it comes from a different body, and often promote tumors. 

Adult stem cells from bone marrow, umbilical cords, and something called “iPS” cells, have been isolated which are just as flexible as the embryonic type, to reprogram to a specific “target” cell type. Other sources of adult tissue are not as flexible, and more difficult to reprogram. But all are your own cells so will not be rejected by your body, and they do not form tumors. Further there is no harm to the donor, and no embryo is killed. Adult Stem cells are “natural” solutions -- they naturally exist in our bodies. 

Most importantly, up to now, no human being has ever been cured of a disease using embryonic stem cells. 

Adult stem cells, on the other hand, have already cured thousands for many years.

They have been used to treat: scar tissue on the heart after a heart attack, spinal cord injury, Leukemia, Parkinson’s Disease, 20 types of cancer; autoimmune diseases, stroke damage, cerebral palsy, multiple sclerosis, sickle cell anemia..… and new therapies are being developed all the time. The latest complete tally of diseases treated found as of March 2021 is Adult :73, embryonic: zero.

Cloning is the process of making an embryonic human being in the laboratory. The nucleus (center mass) of one cell is transferred into a second denucleated ovum and stimulated to divide and grow into a new human being.

A human embryo is a human being, a being that is clearly and unmistakably human. It is not a zebra-type of being, a plant-type of being, or some other kind of being. Each of us was once an embryo, and this affirmation does not depend on religion, belief systems, or imposing anything on anyone. It depends only on a grasp of basic biology. Once you are constituted a human being, which always occurs at fertilization, you are a new member of the human race who must be protected unconditionally. Nothing is added to the fertilized ovum, who you once were, nothing but nutrition.

So Catholic Teaching: First, it is immoral to both make and destroy human embryos artificially. As stated above, each of us once was an embryo, & we are persons from the instant of fertilization to natural death. 

Second, it then follows that embryonic stem cell research and cloning are morally wrong because a human life is killed; Adult stem cell research is morally licit, and is encouraged.

References:

1. What the Church Teaches: Stem Cell Research and Cloning, Our Sunday Visitor, Pamphlet P923; 1 (800) 348-2440.
2. Stem Cell Research, Cloning & Human Embryos, Rev. Dr. Tadeusz Pacholczyk, Family Research Council; 2007; 1 (800) 225-4008; www.frc.org.
3. Stem Cells, Cloning and Human Embryos: Understanding the Ethics and Opportunity of Scientific Research, Dr. David Prentice & Rosa Macrito, Family Research Council; 2013; www.frc.org.
4. Embryonic Stem Cells: where do they come from and what can they do?
5. Check the Score: Adult vs Embryonic Stem Cells, Benefits in Human Patients (Peer-Reviewed Studies), Do No Harm Fact Sheet; www.stemcellresearch.org.