Well if you want just a quick overview of what's happened in the series so far, I'd recommend checking out this page (It's not the best summary, but it'll give you an idea of what the series is about). From there, you could go searching throughout the wiki to understand the series more. Or you could always ask, like Weiss said, our local source of all KH knowledge. You could also look around the forums and ask questions about the series, but in all honesty, I think it's best if you just play the games instead. It'll be much easier for you to understand it.