The last 10 stitches of your knitting will have a separate instruction later, so you'll work your ribbing pattern until there are 10 stitches left on the left needle. You'll put them on a holder (use a safety pin or, preferably, crochet them off with an odd piece of yarn with single crochet if you don't have a special stitch holder). Now if this is the neck edge, when you turn the work you'll work one stitch, work the next 2 together in the stitch pattern of the second stitch, and then finish the row. I'm guessing this is probably a V neck sweater and your button band probably extends around the neck in a different step, so keeping those decreases away from the very edge will be important in the step that has you work that neck band around.