Try to collects as many hearts as your can (within a single run of a level) and complete the levels as quickly as possible to get a higher score for each of the three difficulties. Once you have a positive score, you can submit it to the scoreboard and compare it to everybody else. (Scores less than 0 will show as 0, and you will not be able to submit them.) Each heart is worth +100 score, and each second you take is worth -10 score.