Natural Selection = The process in which organisms adapt better to their environment in order to survive, produce more offspring.
An example of natural selection would be giraffes. Back in the day, giraffes used to have short necks. Since they had short necks, they were not able to eat as much from tall trees. Over time, their necks grew longer, themselves adapting to the environment in which they lived and they were able to eat from those trees high up and were also able to fight any predators that tried to attack them.