To invite new people into your portal, visit the People tool and select Invite People in the center of the page. Enter the email addresses of the invitees, include a custom message, select a group for the invitees to be added to, then submit.
All of your pending invitations are accessible on the right side of the page. Click Manage Pending Invites to view a searchable list. You are also provided the option to Reinvite users. This can only be done once every three days.