Every challenge maintains a leaderboard that ranks participants in the challenge. The ranking is based on the best score achieved by the participants. For challenges such as Time Series Prediction having Root Mean Square Error (RMSE) based error the less the error score, the higher your rank is.
The leaderboard is usually publically visible and can be accessed by going to the challenge page and clicking in the "Leaderboard" tab.
Sometimes the leaderboard may not be made visible to the public by the organizer. In that case, you will be able to see your current rank in the "My Submission" page. You will also be able to see the score of the rank 1 holder.
The leaderboard is updated every time a submission is made by any of the participants.