The theory of evolution would take 10 pages of text to explain my understanding of that theory. But I'm guessing you're not actually asking me to provide that lol.
*If that theory were correct, the monkeys to humans thing is no different than why some primates are monkeys.. and some primates are apes.. and some primates are humans.
My understanding of the theory is that Darwin made the realization that any animal separated by geographical location or independent need, will develop its own skills and traits to cope with said environment. Over an extended period of time, those traits continue to develop into a new species. Even under creationism, the evolution of human traits and minds is accepted, except by groups such as young earthers. As in human fossils we have found, have shown distinct differences in build and muscular tone according to their needs at the time.
Even today, longtime residents of places like Alaska or Siberia, show a much slower rate of heat loss on a thermal camera when taken from a warm environment to a cool environment, compared to those of us who live in a modern conditioned environment. I.e. their bodies have evolved or adapted (whichever term you prefer) but changed from ours, according to their environment.
That has happened in an extremely short amount of time. So I could see the possibility of a complete transformation over a much longer period of time. We shouldn't see that now given our communication and interactions with these isolated groups.
Or, that could be nothing more than simple adaptation with no relation to evolution.
Once again, I am in no way promoting creationism or evolution. Not because I'm afraid of taking a stance, but because I am completely humbled by the question. Some pick a side and go with it, I listen to and read both sides equally and just don't know the answer. You have to have a certain amount of faith in either one. I'm just in awe personally. If I ever feel certain I have the answer, I will state as much. That day is not today