If you want to add users into your organization or workspace that are not yet part of the portal, you can invite the users from Members screen on both organization and workspace.
Click Add member button and choose Invite new member. You can input multiple emails of people you want to invite. Users found in user directories connected to portal will be added automatically, others will be invited to join the portal 1.
User invitations expire after 3 days. You can prolong the expiration date or delete the invitation on the Invitations screen in organization or workspace.
1 Not available for all portal