What is meant by evolution through natural selection

Hello!

Natural selection is the way that animals evolve. 

The theory of natural selection is that the animals that do not have a specific trait to survive in their environment will die. The animals that do have the trait will survive. The animals that survive will then pass the trait down to their offspring, who will also likely survive because they have the trait. This is how species evolve and continue to survive in their environment. 

The species evolve because only the fittest survive (this is known as "survival of the fittest"). The animals that do not have the needed traits will die and they cannot have offspring. 

I hope this helps answer your question! Have a great day!