Sorry don't know the tune but. . . When working with a pulling horse Gee is hollered when you want the horse to pull right. Haw is hollered when you want the horse to pull left.
there are a number of folks around here that still keep and use (mostly for tourists, parades, festival etc.) buckboards and wagons pulled by horses. And a few (very few) that still plow and work fields with horses.
There is even a need for drivers. People who know how to harness the animals and care for them as well as drive them. There aren't a whole lot of us left.