At the end of each game you receive a score on the Results page. You are ranked against your opponents based on your score.
As well as your own and your opponents' scores for that individual game, you can view the monthly high-scores for the game by selecting the Friends' best, School best and World's best tabs. You can see these when you finish a game - the tabs are at the top of the results.
For some games, such as Talent Show, the score is how many questions you correctly answered.
You want this to be as high as possible!
For other games, such as Cycle Race, the score is how long you took to finish the game.
You want this to be as low as possible!