Inside every organism is a code that determines its traits. Things like hair color, height, and eye color are traits. Over the course of millions of years, the genetic code inside organisms gets tiny mutations that slightly change it.
Fruit flies produce baby fruit flies every 10 days. Imagine that over the course of the last million years, there have been 10,000,000 generations of fruit flies. With each generation, there is a chance of new genetic mutations being passed on through reproduction.
Mutations that are helpful to an organism are called adaptations. If fruit flies with longer wings (adaptation) are more likely to survive, they will be able to reproduce and pass on their traits.
The process of fruit flies with short wings dying because they can't escape the birds that eat them is known as natural selection. Over time, tiny mutations become more common if they help fruit flies survive.
Mutations that make organisms more likely to survive being passed down from generation to generation is known as evolution. Zebras developed vertical stripes to camouflage themselves from lions. Vertical stripes as an adaptation to help zebras survive is an example of evolution.