Evolution is not a difficult concept to understand.
look at dogs. There are many different kinds of dog all classified as Dog. Not all dogs are k-9s. All dogs came from wolves. Wolves are k-9. So over a long period of time through breeding all current kinds of dog came from wolves as their common ancestor, but not all are k-9 and those dogs cannot mate with k-9.
this is what happened with humans. Humans and monkeys are primates. They come come from a common ancestor like dogs all come from wolves.
This is the best way I can think of to explain evolution. It's a bottom up design of gradual change over billions of years through which only the good enough to survive will make it and pass on their genes. It's a very simple concept to understand, unfortunately people who want to deny it will never accept it no matter the evidence or logic.