If you are an Office 365 customer, groups in Microsoft Stream are built using Office 365 Groups. When you make a group in Microsoft Stream it creates a new Office 365 Group that can be used across Office 365, giving the group an email address, calendar, site, etc. If you already use O365 Groups in your organization, you can start using those groups in Microsoft Stream right away.
Owner of group
If you are an owner of a group, you can make changes directly in Microsoft Stream.