What is the difference between species and subspecies?
Let me speak first to the position of the last Pope, Pope John Paul II.
In 1996, Pope John Paul II published a "message" where he wrote,
"In his Encyclical Humani generis (1950), my predecessor Pius XII had already stated that there was no opposition between evolution and the doctrine of the faith about man and his vocation, on condition that one did not lose sight of several indisputable points (cf. AAS 42 [1950], pp. 575-576).
Today, almost half a century after the publication of the Encyclical, fresh knowledge has led to the recognition that evolution is more than a hypothesis. It is indeed remarkable that this theory has been progressively accepted by researchers, following a series of discoveries in various fields of knowledge. The convergence, neither sought nor fabricated, of the results of work that was conducted independently is in itself a significant argument in favour of this theory."
It's clear that Pope John Paul II does not reject evolutionary biology.
It's good that we are in agreement that human beings and chimps are not the same species, since they're not. Since chimps have an extra pair of chromosomes, it's extremely unlikely that we could reproduce.
I'm not sure if you looked at my links from the earlier post. I know creationists don't like to talk about plants (I don't why), but there were examples in there of plant mutations that made it impossible for these plant groups to reproduce with the precursor line, but still remain viable among themselves. This is usually how new species begin to form.
You had asked about subspecies. The term is usually used for describing a geographic segment of a species as a way to talk about their characteristics specific to their environment or behavior. However, they are still viable within their species. A non-politically correct usage in humans would be to describe races of men as subspecies, but that's rarely ever done because of historical situations related to black slavery.
There are biologists who don't like the concept of subspecies and they continue to argue against it's use.