Four-foot folio refers to cutting four-foot whole rice paper (specification: 138*69cm) into two pieces, and the folio is divided into horizontal (upper and lower cutting, called bucket) and vertical (left and right cutting, called couplets or banners), which are 69*69cm and 34.5* 138cm respectively.
As for the writing content, if it is horizontal, you can write poems; If it is vertical, you can write couplets or four-character banners.