TPC members have four levels of privilege:

(TPC) chair
The chair manages and configures conference; can inspect any paper. The chair can assign reviewers to any paper.
Track chair:
A track chair can inspect papers, change the paper status and assign reviews to papers within his or her designated tracks. A track chair cannot notify authors, invite TPC members or configure the conference. (As noted, all papers are assigned to tracks when registered.)
Group leader:
A group leader can inspect papers, change the paper status and assign reviews to papers within his or her TPC group. A group leader cannot notify authors, invite TPC members or configure the conference. (As noted, papers are not necessarily assigned to a TPC group; this assignment has to be performed manually by the chair or track chair.)
TPC member
A TPC member can be assigned TPC reviews and may have special privileges to see reviews and to assign regular reviews to papers, depending on the conference configuration. TPC members can be assigned to one or more TPC groups and can register for the TPC meeting. TPC members can be assigned to a specific track and then only see papers for that track.
(designated) reviewer
A designated reviewer has no special privileges, but appears in the reviewer selection list. Designated reviewers do not appear on the TPC listing.

Review questions can be designated as being viewable by role, e.g., only by a chair, group leader or TPC member.

All types of TPC members are only part of the automatic paper assignment if they are flagged as reviewing papers. That is the default for reviewers and TPC members, but not for group leaders and chairs.

TPC members can be grouped into TPC groups, with a group leader. TPC groups are useful for large TPC meetings; they are not, however, used for assigning papers. TPC groups are not visible to authors and cannot be chosen by authors. Each papers can be assigned to one TPC group, so that members of the group can see the reviews. TPC members can be member of zero, one or more TPC groups. TPC group leaders ("groupleader") can list papers.

TPC members can be in one of several states:

chosen:
The TPC member has been chosen, but no invitations will be sent (yet).
notify:
The TPC member will be notified during the next hourly notification run.
invited:
The TPC member has received an invitation or is treated as if he or she had received an invitation.
accepted:
The TPC member has accepted the invitation and is now an active member of the TPC.
declined:
The invited TPC member has declined the invitation and is not an active member of the TPC.
noresponse:
The TPC member has not responded to the invitation. This status is set by the chair.
invalidemail:
Email to the TPC member has bounced as undeliverable.