Question: Hi. Why are monkeys still alive if humans are their descendants?

Hi! This is a really good question, I’ve always found the theories of evolution fascinating!
However, it’s not exactly true that humans descend from monkeys, but this is often used as a simplified explanation, which then causes some confusion.
Millions of years ago, both humans and monkeys evolved from a common ancestor which is now extinct. In our perception, this ancestor would have probably looked more like a monkey than a human, but in reality it was actually neither of those.
To use an analogy, it could be a bit like saying that monkeys and humans are “cousins”. In fact, they descend from the same ancestors (e.g. their “grandparents”), but they have different “parents”. These then create two new related but distinct lineages which will both keep existing.
More generally, if a species evolves into another one, the one that it evolved from will not necessarily go extinct. This will happen for example if the two species compete against each other and one of the two prevails, but the “original” species will not necessarily die out and they could both coexist.
That said, I’m not an expert in evolution, so there are probably more complicated and accurate explanations! But hopefully this will give you an idea.