The lore and story behind Dark Souls is notoriously impenetrable. I should know. I just spent 52 hours completing the game and I know next to nothing except I killed a bunch of dudes and broke and Xbox 360 controller in the process. The above video goes to some lengths to try and explain what the hell is going on in a humorous fashion. As a primer for the upcoming Dark Souls II, I think you should watch it.
But if I'm being honest, I'm now more confused than ever! This game man, this goddamn game.
Even if it does confuse you -- and chances are it probably will -- it's still good viewing, and might help fill in some gaps for the people who obsess over Dark Souls and its lore.