If you would like to view the game leaderboards for a certain game, you can do that by visiting the “Games” tab. After that, simply click on the game you are interested in and you will be able to see the leaderboards on the next page.
Here you will see how you rank against your friends, but also against all other players of that particular game. You can view the top scores for today, this week or all time. By clicking on a person you will have the option to send them a friend request, if they are not already your friends, or challenge them.