The Staff page replaces Access Control in Stellar. From here, users may be added to various standard staff roles, including Admins, Instructors, TAs, and Graders, via the "Add (Role)" panel on the right side.
If sections have been created, you may optionally assign staff members to certain sections. If a staff member is assigned to a section and the "Global" course-wide access checkbox is unchecked, that staff member will only have access to Learning Modules content (including Gradebook Module) pertaining to the students in the assigned sections.