For contacts managed within the PIRS address book there is one field value for which you can maintain a list of keywords, the contact type.
As indicated by the screenshot of a contact in read mode below, the contact type defines the role of the respective person within the project.
You need to define at least one keyword for the contact type.
In order to change keyword values or create new keywords simply select "Contact Types" within the administration navigation and proceed as described in chapter Manage Project Keywords.