From 'Users & Groups' --> 'Users' --> 'Create new' you can add new users to the account by filling in the name and email address. The new user will receive an email to set a password for his account.
You can also change the role of a user or add them to a specific group.
From 'Users & Groups' --> 'Groups' --> 'Create new' you can create or remove groups. Groups help you have different types of meeting assigned to different users.