Multiple of 12 + 3 Colours A & B.
Cast on with Color A and k one row.
Row 1 (RS): With Color B, k1, ssk, *k9, slip 2, k1, p2sso; rep from *, end k9, k2tog, k1
Row 2: With Color B, p1, k1, *p1, k4, (k1, yo, k1) in next st, k4; rep from *, end p1, k1
Rows 3 and 4: With Color A, Rep Rows 1 and 2
You just need to carry the yarns up as you knit. There are many great tutorials on YouTube for this.
As you can see below I'm having fun mixing colours right now!
It is a lovely stitch that could also be used to knit a scarf although the wrong side is not as neat as the right side. The number of stitches needed totally depends on the yarn you'll be using and how wide you want your scarf or cowl to be. Knitting a few rows to see how it looks will be the best thing to do.