Embryonic stem cells are cells in all organisms which are capable of producing every single cell in the organism. They appear a few days after the fermentation process and produce enough cells until birth, and are then on no longer available. Scientists are able to learn a great deal using these cells, but the studying/usage will result in the death of an embryo.
Adult (Somatic) Stem Cells
Adult stem cells, unlike embryonic cells, can only produce a limited variation of cells in the organism. These are found in the tissue and are used as a repair system (Ex. closing of wounds). They are bountiful especially in the bone marrow. The cells can be harvested and used in many medical treatments, such as leukemia and blood & bone cancers. The harvesting does not cause deaths of embryos.
Induced Pluripotent Stem Cells
Induced pluripotent stem cells are adult stem cells reprogrammed to have some of the traits of embryotic stem cells by using viruses. This makes it so scientists must carefully test any IP stem cells for human use as it caused cancers on some tested animals. Despite that, scientists are working towards using it as a transplant medicine.