The first time you enter leaderboards you will need to verify your information and opt in. Your handicap and nationality will be pre-populated and you can make any necessary changes using the drop-downs. Once you are happy with the information you must tick the box to agree to sharing data and then press the 'Compete' button.
If you no longer want to take part in leaderboards then all you have to do is opt out. This option is contained within your account settings on dashboard. Once you have opted out you will be removed from all leaderboards that you were competing in.