If you own a group or if you have a manager role in a group, you can add people as members to the group.
Groups are managed using your web browser interface. You can use groups on your mobile device (add them as members to folders and conversations and so on) but you can’t add people to groups using a mobile device.
To add someone to a group, click Groups in your user menu. Open the group or click next to the group name, then click Add Members.
You can add individuals or you can add other groups. If you add a group and a person is in that group, you won’t be able to add the person as an individual.
When you add an individual as a member of a group, you assign permissions to them, either as a manager or a member of the group. If you add a group as a member, the permission you assign to the group applies to everyone in that group.