Members and roles
Invite people, approve email domains and set roles.
Members are owners, admins, members or guests. Invite people from Settings › Members, and change a member's role from their row's menu.
With approved email domains (Settings › Security, each verified by a code mailed to an address at the domain), anyone with an address there can join without an invite.
Guests and private teams aren't enforced yet
Every member and guest can see every team's issues, comments, projects and documents, private teams' included. Don't rely on either to keep data from someone. Guests don't see initiatives.
A workspace's data region is set when it's created and can't be changed.