You've hit right on the spot with this question. The thing is, no one knows for sure where words come from. There are three explanations that scientists are divided over.

Remember evolution lesson? Some scientists think that cavemen who could talk better, had a better chance of surviving. Now imagine you're a caveman some 200,000 years ago and you see a huuuge tiger who wants to eat your family. If you tell your family (by yelling or screaming), you can save your family. If you're not good at yelling or screaming, your whole family will probably be eaten. Do you see where evolution comes in? Those who can communicate better pass on their genes to their children.

Another answer, scientists say, is that it's a result of human skills, such as planning and memory. Scientists who believe this say that language happened as a result of humans planning, thinking and memorizing. Think about the wheel: Who invented the first wheel? Someone probably happened to stumble upon the idea of a round wheel. The same with language. At some point, people started to memorize certain yells or screams. Over many thousand of years, words developed.

Another answer is that the brain allows humans to create language. These scientists say that there is some piece of brain that allows humans to easily create and understand language. Scientists who believe this say that this "talent" is with you at birth.

The important thing to take away from all this is that there are many answers. The above answers should give you an idea of what scientists believe. Now, what do you think? Do you believe the scientists? Do you have a better explanation? Give it a shot!