In simple terms, what is evolution?
Evolution is the gradual change of an organism to adapt to its environment.
Assume that we transferred a group of 50 humans to a cold place to live for 100 years. Some of those 50 human beings would have a low tolerance to cold and would die quickly. Some would be naturally able to tolerate cold. That's called having the "trait" of being able to handle cold weather easily.
Now if you have children with another person within the survivor group who had similar traits, the chances are that your child would have an excellent chance of surviving the cold weather, because they inherited those traits from you and your partner.
What I just described is called "Natural Selection", and is what Darwin's theories are based on.
Whether or not you believe that God created us all and everything in its place right now, Natural Selection is all around us every day, from plants to animals, and of course over longer periods of time, human beings.
It means that species would change over time, and that theory was introduced by Charles Dwarin.