Shapefile with Excel Data Dictionary

I'm working with a shapefile dataset I received from a 3rd party. All string fields are 2 digits long and have 2 letter coded values. Accompanying this shapefile was a data dictionary in Excel format. I don't ever work with domains, so I'm rather clueless as to how to go about this. How would I get the descriptions for these coded values into this shapefile, or would I have to first add the data from the shapefile to a gdb as a feature class and go from there?

Thanks,
Mike