I downloaded the data tables and the GIS boundary files. Now how do I join them together?

I downloaded the data tables and the GIS boundary files. Now how do I join them together?

NHGIS has made it as easy as possible to join data tables to their respective GIS boundary files. In both files, you will find a field called GISJOIN that will serve as the join field. Additional information on using a GIS with NHGIS data can be found on the User’s Guide page.