Summarize this article in one sentence.
Place the middle of a koshihimo across your belly just above your hip bones. Wrap the band around yourself and cross the ends behind your back. Then bring them to the front and tie a tight single knot. Koshihimo are thin bands that hold the fabric in place; typically, 2 are used to secure a yukata. Unlike the ornamental obi sash, koshihimo are hidden. One is tucked away under extra fabric, and the obi goes on top of the other. Straighten out the collar and make sure the garment is tightly wrapped. Then fold extra fabric over the koshihimo to hide it. Be sure to tuck away the koshihimo in both the front and back. Double check that the fold you made over the first koshihimo is straight and the yukata is snugly wrapped. To secure the top of the garment, tie another koshihimo just below your rib cage. The obi will cover this koshihimo, so there’s no need to fold fabric over it.

Summary:
Tie a thin koshihimo band around your lower waist. Tuck extra fabric over the first koshihimo. Tie a second koshihimo around your upper waist.