It's a way of temporarily holding stitches. You will come back and work them later. Sometimes stitch holders that look like giant safety pins are used for this. Since this probably is round, that's why they want you to put these on a piece of scrap yarn. Use something that's different colored than the yarn you're using so you can easily pick these stitches up again. You can also use several bobby pins to securely hold these stitches if you want to.