World Challenges (W.C.) are games that you play against other people. Let's take me for example. I can enter the World Challenge for Typing Terror. I have to pay 100 Neopoints to enter the competition and I play for an hour against other people. I can submit my score as many times as I would like in that hour. The minimum number of scores to enter is 3. Each score you submit is paired with another person's score. If your score is higher than the other person's, you earn a win. If your score is lower than the other person's, you get a tally in the loss column. To win a piece of the map for the place in Neopia where that game is located, there has to be five people playing and you have to have a positive number of wins (in a nut shell). Basically, if you only enter 3 scores for that hour, you have to win 2 or 3 of your games against random opponents. Sometimes you can get away with winning only one game, but it doesn't happen too often. I'm sure there are other people here who can explain it a little better. I've posted a couple things below to help you also!
From Neopets:
"World Challenges are competitions against random, unknown opponents to see who can get the most wins in an hour.
The player with the highest tally of wins (and meets all game requirements) at the end of the hour wins neopoints from the jackpot as well as a piece of a picture.
Every game that is in a world challenge will have the little world icon at the bottom of the game page. There is also a link at the bottom of the main games room page."
http://www.neopets.com/challenges/main.phtml
Also, here is the FAQ page:
http://www.neopets.com/s/index.phtml?tr ... int_id=419
And here is the newest PPT thread about the recent changes:
http://www.pinkpt.com/forum/viewtopic.php?t=24508