A theory in the scientific sense is a mechanism that joins facts together in such a way that it is able to make predictions that can be verifiable. Without theories, science would be dead. They allow for us to draw conclusions from the raw data, the facts. The theory of relativity changed the way we thought about motion and our concepts of Time and Space. It is probably one of the single most important ideas in the history of Science.
All materials here are as accurate as the author knows.
There are numerous works out there that probably explain the Theory of Special Relativity better than I can. I encourage everybody to learn more about this.