Oh, don't feel bad:) I'm (fairly) new to LJ too and I didn't know what the heck they were either.

Basically, you're put into teams and you 'battle' each other. There are games like trivia challenges and anagrams. There are also challenges for icons/graphics, fics, and vids. You get points for (almost) every challenge you complete and at the end of several months, those points are tallied and one team is declared the winner.

There are no real prizes for the winning team, beyond bragging rights, but it's a great way to get involved in your favorite fandoms and meet some new people.

whedonland is the one I've been involved with the longest and, in my opinion, the most well-organized. The BSG comm, twelvecolonies, is pretty nice but so far, has run at a much slower pace than whedonland. wholand and bonesland haven't been up long enough for me to really say much about them.