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 'External Recruiters' tab as displayed below.
Next, click to '+ Invite New Recruiter':
Now you need to add them like you would any other user, be sure to assign their visabilities to ensure they can see the jobs you want them too. They will receive an invitation to their email with a link to finalise their account setup.