Open Settings → Users & Roles.

The tabs
Tab | What's there |
|---|---|
Team | Everyone in the tenancy: their tier, roles and status, and pending invitations. Invite someone is here. |
Roles | The tenancy's roles and the permissions each one grants. Create your own roles here. |
Workflow roles | Who holds which roles in each feature's workflow. See Workflow roles. |
Activity | Who changed what, and when. See The activity log. |
Tiers
Each member has a tier: Owner, Administrator, User or View Only. It's a label that says roughly what someone is; what they can actually do comes from their roles.