The Project Directory is your list of participants on a particular Project
To add a new User, click on the Add User button, and follow the wizard.
Until they accept your invitation and accept the Duties and Responsibilities assigned to them, the Collaborators you invite to a Project will appear in the "Invitees" directory, once their Role on the project has been accepted they will be added to the main Project Directory. Until the user has accepted their legally appointed role on the Project they cannot be considered to have been properly appointed.
You can edit the Roles or Disciplines attributed to users via the Directory, as an admin level user, simply click Edit on the user's entry in the Directory.
Editing Invitees can be done any time, editing a User who has accepted their invitation will send them a notification that you have suggested changes to their profile, and ask them to accept the changes.