To add a new group, go to Space Settings > User Setting > Group, and then press the "Manage Group" button from below where it says List of Groups.
Then, proceed to the Group List Screen on Nulab apps. To make a new group, click "Create new group":
You can see a list of a group's members by clicking “View” next to the group name.
For more detailed information on groups, please refer to "Listing and Creating Groups" in Nulab Account Help.