I know they do...just..I don't understand fully how it works and why it is free to use.
I recommend reading Free Culture by Lawrence Lessig. It explains everything you need to know about copyright. The question shouldn't be why its free to use, but to ask why certain things aren't.
As described in the book, the point of initially introducing copyright was because "society" thought that it would encourage writers to write more and quality would increase... which most people thought would be for the benefit of everyone. It is a trade-off between limiting our freedoms and getting more good stuff to consume.
That's still the official motivation for keeping copyrights in place, and if you think of it that way, the copyright laws we have will make sense, regardless if you agree with them or not. At it's core copyrights is simply this trade-off. It's got nothing to do with natural rights of the creators or anything like it.
Ideas, like Veinglory pointed out, spread virally in cultures and copyrighting them has got liberal democracy/free speech legal conflicts. That's a can of worms we don't want to open.