The app is populated with multiple challenges for you to join. Sometimes these challenges are for prizes, rewards and sometimes just for kudos.
To see all of the challenges that are available to you, hit the medal icon navigate to the challenges screen in the app. To join a challenge, simply tap the challenge description and hit join.
Once the challenge starts, you can monitor your progress and see where you rank on via the leader board. To do so, go into the challenge and tap ‘rank’. You can then filter the leader board by your gender, age group, organisation or team.