Groups is a feature that allows you a more personalized app experience with your Friends / Family / Colleagues.
Groups make it easier to interact with others in your group rather than everyone on the challenge.
How they work:
You or another user creates a groups and invites the relevant people.
Once you join you can access the group from the My Profile screen.
If you like you can also choose the map filter on each challenge to only show people from 1 group on the map (optional).
Benefits of Groups:
Privacy - you can set your privacy to restricted, which will then allow only people that are in a group or team with you see you in the app.
Interaction - allows you to interact with others in your group in a private newsfeed within the Group.
Customize - You can be a member (or admin) of multiple groups. This way if you are doing more than 1 challenge you can share and interact with each group differently.
You can see how friends are progressing on challenges that you have not joined