A granger is a farmer. If you want to be a granger one day, you might get a job on a dairy farm or go to agricultural school.
While the twelfth century word granger isn't used much these days, it was a common way to refer to a farmer in the late 1800's United States. The noun granger comes from the Old French grange, "barn or farm house," ultimately from the Latin granum, "grain." The word grange came to mean a US farmers' association which worked for the rights of small farmers and built Grange Halls across the country for grangers' meetings and gatherings.