A rendar is an official or landlord. Either way, a rendar is usually an authority figure.
Accordingly, a rendar can preside over an estate but may not own it. In ancient usage, he may lease the estate from a lord and collect rents on the lord's behalf. Today, a rendar could be a landlord or even innkeeper. He can make decisions on any issue connected to the piece of property that he presides over.
In the story, Gitl makes sure that all the wedding gifts for Shmuel and Fayge are piled onto two wagons. Among the gifts are crocks of butter, wooden bowls, and lengths of cloth. Apparently, the rendar himself sent a gift, albeit not a pretty one: a pair of silver candlesticks.
All of the main characters that Hannah meets in her mysterious world live in a shtetl. In Eastern Europe before World War II, most of the Jewish population lived in shtetls. In the story, the rendar would have presided over the land and shtetl. He would have been an authority figure in Shmuel, Fayge, and Gitl's world.
Source: The Classic Yiddish Stories of S. Y. Abramovitsh, Sholem Aleichem, and I. L. Peretz, edited by Ken Frieden (2004)