BO however many sts for your size (3, 4, ?) then when you get to the sts that make up the cable k3, dec 1, k3 and work across to the end of the row. Turn and BO X sts, when you come to the purl sts that are in the cable section p3, p2tog, p3 and finish the row. Next row, BO your sts, and by now the first cable is probably bound off, when you get to the next one, k3, dec, k3 and work to the end of the row. Turn and on the WS, BO sts, work to the cable stitches, p3 p2tog, p3. That's actually 4 rows and you should be done with binding off - put the remaining stitches on a holder and you're done with the back for now.
There's a good picture of the back neck and shoulders on this project at ravelry.