The second line under the "Back" instructions tells you how to do the twisted rib (sounds like a new dance step, huh?):
Twisted Rib: Row 1 (RS): P1, * LT2, p1, rep from * across.
Row 2: K1, * RT2, k1, rep from * across.
Above that in the sitch Glossary are the directions for LT2 and RT2.
Basically over 7 sts you'll have p1, LT2, p1, LT2, p1.
That'll give you that nice double mini cable that is featured in the close-up photo.