Leaderboards post your total score of each level, showing either on the Global, Friends, or Single User tab in the Level Selection menu. On the bottom right corner of the screen, there is a Leaderboards button. Selecting the button will turn the icon blue. You are now in Leaderboards mode. From there, you can select any level to see the posts for that level. Also in Leaderboards, you can enter the selected level by selecting the Play button.