The Settings -> Job Titles area allows you to view, edit, delete, and create job titles, which can be used to describe / categorise site contacts.
To add a new job title, select the Add Job Titles button at the top-left of the page:
This will create a new row in the Job Titles list for you to populate with a new Job Title. Select Update in order to save the new title and add it to the list.
You can also Edit and / or Delete the Job Title information once it has been added to the list.