When you are tracking a lot of metrics with Radar, groups let you organize it better. You can create a group and add one or more metrics to it.
You can select a group from the top-left menu button or by right-clicking the Radar icon in the menubar. After selecting, only the metrics belonging to the group is listed.
To go back to listing all the metrics, you can select 'Show all' from the same menu. Options are available to create, rename, edit & delete groups.