An external recruiter is only able to add candidates to jobs that you give them access to. They can't see candidates that they did not add themselves, and they cannot be assigned roles.
First, browse down on the Pinpoint dashboard and select 'Team' under the 'Company' section, then click on the 'Recruiters' tab as displayed below.
Next, scroll down to the 'Invite External Recruiter' section:
Enter their First Name, Last Name and Email, then click 'Invite'. They will receive an invitation to their email with a link to finalise their account setup.
Once you have added a recruiter, you can manage what jobs they can view through assigning them Locations and Departments. See How to Add/Edit/Remove a Team Member's Permissions.