I've played Kingdom Hearts, Kingdom Hearts II, and Chain of Memories, along with 'Days' on the 3DS (big mistake on that one).

I've tried to read some summaries to connect all of the games (including Birth by Sleep and everything else I've missed), but I'm just lost. I don't want to say that the game is a convoluted mess or anything, but I honestly can't decipher all that much. Things that seemed pretty simple have now been opened time and time again, so I guess I'll just bring up some general questions.

Mainly, I want to understand all of this so that I can enjoy Dream Drop Distance in peace. I would play Birth by Sleep, but I am way too lazy to invest in a PSP at this point in time.

So, without further ado:

Could someone summarize the events of the series? (Can be as brief as you want)
Who the hell is Ansem (since his story has been expanded like crazy)?
Why do Sora and Roxas and the dude from Birth by Sleep look identical?
Who is Xehanort, and why is he alive at many different ages throughout the various games?
What is the X-blade?

I understand that some of these can be answered by google, but I've tried and I've ended up even more confused than when I was clueless. I'm assuming that my asking these big questions in one post, it will make a little bit of sense.

Thanks!