Vampire Diaries question

Since so many of you seem to like this show, I gave it a try, and in fact like it very much. It's on a channel I get here and we're up to episode 17. But since I have not watched it from the beginning, there are things I do not understand, like ( spoilers for episode 17 under the cut )

Please don't spoil me for anything still to come! I don't care too, too much, but it just would be a bit nicer.