What is opac authorities module
Opac authorities works like the main module opac but allows importing authorities instead of biblios. The other difference is that it make imported authorities, not nodes, but entities. Opac authorities provides authority entity and authority type (bundle) entity.
Opac authorities is also a plugin for biblio mapping (see Harvest plugins documentation). The authority plugin allows to link authorities with biblios when harvesting them.
Create authority type
Go to admin > structure > authority-types and click on Add authority type. Enter a label, a description and save. Authorities are fieldable, so you can add as many fields as you want and of the type you want by going on manage fields link.