We have two main types of documents, which are described in the Item Type Metadata tab.
Text is used for any textual document — letter, report, flyer, etc.
Person, Organization, Law are used for identifications of people, organizations and laws.
Moving Image is for videos or movies
Oral History is for transcripts of interviews with figures in the movement.
Sound is for audio tapes or files.
Still Image for photographs or image-based flyers, etc.