Can a single stem cell only create one other stem cell ?

Cells multiply by splitting up, so I would say yes. Of course, after that, the new cells can divide again.
That’s how a single impregnated ovum grows into a human.

Yes, the cell divides into another cell. However it is capable of differentiating into other cell lines, which is what makes them medically significant.

This question could be interpreted a few ways. One cell divides, and it become two, then those divide, and it become four, and so on. All the cells are identical having the same genetic material. However, as @cockswain pointed out, stem cells can differentiate. If you think of it like an embryo, the first couple of weeks all cells are identical, undifferentiated, and then they start to differentiate, become the eyes, spine, legs, etc.

Further, embryonic stem cells can become any cell type. Adult stem cells can become many, but not all.

To learn the facts about Stem Cells visit american'sforcure's.org

Wait a second? How was my quip off topic? Dr_C is leading in stem cell research. wow

I would say that the cell, after undergoing mitosis, would split into many.