Rinse beef, remove tendons, and cut into desired size.
Before cooking, pound the beef with a meat tenderizer or the back side of a knife to keep the beef from curling up during cooking, and to make it more tender.
When cooking pressed meat, tie it up with kitchen string to make a nice shape, and boil.
Source
Source: The beauty of Korean Food: With 100 Best-loved recipes by institute of Traditional Korean Food